newbie css and ssi problem

[Rookie]

My first attempt at css (& ssi for that matter) I made
this page that only works in netscape and opera
- for some reason IE5.01 won't display it correctly

Apparently I've completly messed up my css syntax,
could someone please look at my code to tell me what
I did wrong?

At first I got it to work almost like I wanted, but
for some reason if I change a line I get this:


http://heftyhosting.com/earncommission.html

the page combines both ssi and css
the ssi pages are:

http://heftyhosting.com/header.txt
http://heftyhosting.com/footer.txt

I had the css linked to main.css but put it back to css
on the page itself to see where I'd gone wrong

Many Thanks

David Bruce
I've not posted here in quite a long time...
I've really missed you guys:)