5
Hi,
If you have a "good" theme, you must have, at least, two css files, one for IE and one for mozilla/netscape.
For your problem, search on this site but I think that there is a hack for two different versions of IE, IE 5 and IE 6.
You should also submit your website to a web validator, you will find one here :
http://validator.w3.org/Give it your web site url and it will shows you the "errors"
Bye,
Hervé