1) You just make it like every normal HTML page. Just be sure to name it either "index.html" or direct you domain to the page, so it's the first page showing up.
Also be sure it has got a useful purpose, since people tend think splash pages are useless.
2) Can you please rephrase you question? I don't get what you mean.
You center stuff using the <center> tag, but it's deprecated (and everyone hates that which is deprecated), so you're better off using <span style="text-align:center;">. I know it says "text-align", but it can align images too.
You can use a Content Management System (or CMS, for short) to be able to post stuff on your site without writting tedious coding yourself. I don't use a CMS, but I know a lot of people are satisfied by CuteNews
You have no subtlety, AgentChronon; you do not recognise fine distinctions. The fact that it "shows up right" on major browsers does not mean that it's valid code.
I'm not saying you shouldn't use it, I'm saying that it's pointless to argue around the irrefutable fact that it causes error - I was just suggesting that because it'll cause errors under certain DTDs whereas text-align won't, it's better to use the latter. That's all.