Your site doesn't work well in IE6 either.
That top nav is pretty primitive coding, would it not be better to make a css one? Or at least get one from a site.
As for the other stuff, you always want your header at the top even when you scroll? I wouldn't bother, it's just annoying and what it the viewable area on my rubbish low res pc is almost zero?
I'll look at the centering when I get home tonight, there is a way to do it using auto margins with a wrapper div.
Where is your attempt at a form? There are loads of tutorials on how to do this.
Life is like riding a bicycle - in order to keep your balance, you must keep moving.