So yea... this site doesn't validate... but it's mainly due to bad coding if some plugins we use and in the posts themselves on the blog. So where possible shut your eyes to these errors.
If there is a simple fix to this problem I'd be happy... basically it looks just about how we want in Firefox on the sidebar... http://www.obsessedwithfilm.com/ but if you look in IE7 the problems appear.
EDIT: Just noticed another problem, this time in IE6 (I don't usually have access to IE6 so hadn't noticed). The navbar background doesn't seem to appear, meaning you can't see the text (unless you hover).