Help fixing an IE CSS issue...

I've been chugging at this for a while, and I can't seem to get it working. The style I hacked together works fine with Firefox, but I can't get it to align properly in IE. I would love to know if anyone could help me figure out what the issue was, and how to fix it.

These are the forums: http://abstract3.com/forums/

Stylesheets:
http://abstract3.com/forums/style/a3.css
http://abstract3.com/forums/style/imports/a3_cs.css

They're modified slightly to get the image header using the known tutorial, however, I can't figure out how to make it center. I wanted to avoid using actual image code within header.php, trying to do it all through CSS, but it's giving me too much grief. Hopefully one of you more intelligent people can fix it

Please only reply if you have something useful to say Thank you in advance, even if you just take a look at it (and mock me).