Bulk brings up a point about most new people getting confused when they're starting the Megaman/Rockman series. The same happened to me about three-four years ago when I got Megaman Battle Network 3, and now, several years later, I still don't understand what's going on in the other Megaman series.
To answer one of the other questions, Rockman is Megaman's Japanese name. Yeah, I'm assuming you went and looked through the Megaman Club and found out that most of us were using the name Rockman and all those other Japanese names instead. Yeah, some of us are like that. :/
As for your main question... This is a hard one to answer. I'm likely only going to be able to give you a definite answer of the Battle Network and Ryuusei no Rockman (a continuation of the Battle Network series just starting in Japan, no English name has been given yet) series seeing as that Megaman series is the only series that I have true experience in. Try heading over to the Megaman Club (link at bottom of my signature) to get info on the other series. I'll try my best at telling you what I know about the other five series though.
Classic Series:
The start of the five-part series timeline. All of the five series in the timeline are platforming and action games, as far as I know. I don't know much about this series, except that Dr. Wily wanted revenge on the world for some reason, so he built several 'Robot Masters' to protect him as he was planning. Dr, Light built Megaman to protect the world, and thus, Megaman was the first robot to gain emotions and feelings... I think. That's about all I know, other than the fact that the end of the series ended on a cliffhanger. :/
X series:
The second part of the five-part timeline. Several centuries after the conflicts between Dr. Light and Dr. Wily, robots and humans have been able to coexist in a world named Neo Arcadia, until a virus that infects robots dubbed the 'Maverick Virus' begins making the robots go berserk. The situation gets so bad that the whole of Neo Arcadia gets plunged into a war. A group of robots formed an orginazation, dubbed the 'Maverick Hunters', to find out how the virus formed and eradicate it, as far as I know. X, apparently a more advanced version of the original Megaman, is the leader of said orginazation. Apparently, there's almost nothing that connects this part of the timeline to the Original series, but there must be something that does connect it that I don't know about, otherwise other fans wouldn't be saying so.
Zero Series:
A direct spin-off of the X series, and the third part of the five-series timeline, detailing the events of another major crewmember of the 'Maverick Hunters', the robot Zero. As far as I know, the situation is pretty much the same as the X series, but through the eyes of Zero instead.
ZX Series:
The fourth part of the five-series timeline, this tells the story of Neo Arcadia after the events of the Zero and X series. The Maverick virus had been eradicated, or so everyone thought. The lands outside of Neo Arcadia are still in conflict, and the two crewmembers in a company that ships packages to the outside lands are about to find themselves in the middle of another conflict. Both crewmembers are named Vent and Aile. The truth is, as you probably already know, ZX hasn't been released in the US yet, so that's why I really can't say much about this.
Legends Series:
Uhhh... This series, I know absolutely nothing about, other than that it probably takes place centures after the events of ZX and that it's probably the final part of the five-series timeline unless Capcom decides to tack a sixth series onto the timeline. I'm assuming this series ended on a cliffhanger too, because Capcom decided to scrap this series due to poor sales. There's hope that this series will continue though, someday,,,
Battle Network:
Alright, this is the series that throws most Megaman fans off. Not only is it an RPG instead of a platformer, but this series, along with the continuation of this series named Ryuusei no Rockman, has no connection at all to the main Megaman timeline. This is a second seprate RPG-based timeline, as most fans can say. The Battle Network series could be said as an opposite of the Original Series. It is also said that this series is supposed to reflect real-world situations (use of the internet, radio waves, conflicts between countries like Japan/Electopia and Russia/Sharo, etc.) a bit better than the other timeline.
The Battle Network series starts with someone named Dr. Light (again, Original Series refrence) and Dr. Wily as friends. Dr. Light researched internet technology, and Dr. Wily went in the way of Robotics. Soon, both needed money for their research, but the congress of Japan or whatever that was would have to choose only one scientist to fund. Dr. Light was chosen, and Dr. Wily, insane with jealousy and rage, began to plot his revenge on the world or something like that. The devices that he made within that time were deemed too dangerous, and so, Dr. Wily was banished from the scientific community.
Fast forward to about several years later, in Japan's famous scientific research center, SciLab. Dr. Light began working on a prototype of the Internet, codenamed 'Alpha'. Another scientist, named Dr. Cossack, began trying to make the first independent Net Navigator (NetNavi for short), named Forte.EXE/Bass.EXE. Eventually, Alpha began malfunctioning, and everyone thought that Bass.EXE was at fault. What they didn't know was that Alpha was riddled with bugs, but it was too late by the time they realized that Bass was not at fault. Bass was nearly killed by the other NetNavis as he escaped into other parts of the Internet, and also began to plot his own revenge on the world of humans. In the meantime, by the time they discovered that Alpha had been riddled with bugs, Alpha had gained some sort of Artificial Intelligence, and Alpha's bugs began to absorb and destroy all of the other internet areas. Alpha suceeded, but was captured and sealed away by everyone in SciLab, and a 'Guardian' program was put in place to prevent Alpha from escaping. Thus started the 'Alpha Rebillion', which lasted for six months. The Rebillion was the time in which all contact with the Internet was shut off. It isn't really known how Bass survived this event.
Fast forward to about one or two decades later. Dr. Light Hikari has passed away (one could assume that he did), and Dr. Yuuchioro (not sure on the spelling of the name) Hikari has inherited the Hikari lineage. The internet at this time was fully operational, with almost every device in the real world connected to the internet. Dr. Yuu also had a wife and sons himself, with the sons being twin brothers named Netto/Lan Hikari and Saito/Hub Hikari.
[SPOILER WARNING REGARDING YOUR LAST QUESTION]
Now, you asked a question, 'Is Megaman Human?' Apparently, in this series, yes. Now, Hub was born with HBD (It probably stands for Heart Blood Disease or something like that...) that ended his life while Lan was unaffected. Dr. Yuu went into some kind of depression after that, but finally decided to get some of Hub's DNA and change it into binary code to create Rockman.EXE/Megaman.EXE, and gave the NetNavi to his other son, Lan, afterwards. It'd take several years until Lan would finally know that Megaman is actually his twin brother.
[END SPOILERS]
You could actually start the Battle Network series on any of it's six games and not get confused at all. The storyline in the Battle Network series is nowhere near as complex as those series in the main timeline, and the games storylines aren't that tied together. After all, after every game, what bugs most people is that almost everyone in the game forgets what happened in the previous game except for some of the main characters. :/
Ryuusei no Rockman/Rockman of the Meteor Shower (direct translation):
Uhhhh... This one is a continuation of the Battle Network series, taking place centuries after the Battle Network series. A new person, named Hoshikawa Subaru, lives his life in a 'Radio Era', just as the previous series was the 'Internet Era'. Radio waves have since replaced the internet, and instead of devices being connected to the Internet world, the Radio World is actually floating above the real world, except it's invisible unless you use something called the Visualizer to see the Radio World. When you're actually in the Radio World, you're considered as 'On Air', intstead of being 'Online' like in the Battle Network series.
Hoshikawa Subaru's dad had actually dissapeared several years earlier, and while he was on the rooftop of school one day, pondering exactly where his dad is, when an FM (think of it as the Radio Era's version of NetNavis) from outer space, named War Rock, appears before Subaru, claiming to know about his dad. Enemies have chased War Rock to this world, and Subaru is forced to ally and temporarily fuse with War Rock to fight them off. Not much is known about the storyline after that, since Ryyusei no Rockman hasn't even been released in Japan yet, nor will it be released until sometime in December.
Again, I don't know much about the games in the main timeline, so you might want to ask around at the Megaman Club and see if the resident Main Timeline experts can answer your questions.