I'd look closer at your stylesheets:
background: #D5D8E5 url(../../images/gradients/gradient_panelsurround.gif) repeat-x top left;
these kinds of relative URLs are likely to get you in trouble when using files outside the normal directory structure. I'd change them to absolute paths like:
background: #D5D8E5 url(/forum/images/gradients/gradient_panelsurround.gif) repeat-x top left;
You can see the vB3 mapping of style variables at the bottom of the forums/vb3.php file.
Please do not PM me for support or sales questions. Thank you for your understanding.