Note Books or Notebook with a Tablet mode. Decide if you want the tablet functions, They cost extra, but you may find them extremely useful. Personally, I'd would get one, if I ever got one. But My Brother would not get one.
For games, Tablets can hinder, especially the older games. It does help with others, so it's not all bad, My best Zurg Rush was with a tablet.
I have a Desktop PC with a graphics tablet, and several PDAs. So I do have an idea on how they work.
With XP-Tablet Edition, and Vista, you get a on-screen-"input" options. They are Handwriting, Letter writing and On-screen-Keyboard. You can actually surf and post on forums like this this one just using the "Pen".
I know Vista has a Gesture system called Pen Flicks. This allows you to scroll & do commonly used commands with ease, and works in most programs.
As for the said input, Handwriting and Letter Writng mode uses spell checker to guess the word, It has trouble picking out words such as Pokémon, Serebii and Pikachu, But you can add words.
Tablets are often useful in Graphic programs.
Like the DS, you'll need to set up the tablet/Screen when you start it up. Probably Very much like new DS.
Yeah, External Hdd space can be cheaper than internal for Laptops. Partly you're not trying to fit 300Gig in a smaller space than most HDDs, but they are slightly slower.