I've just uploaded the latest version of the Virtualmin Framed theme, which corrects many minor issues in Internet Explorer, and also fixes a large number of validation issues with the HTML and CSS. The theme now works well in all major browsers, to the best of my knowledge. It is also quite a bit cleaner, and seems to render faster on all browsers as well (probably due to the removal of a number of errors in my HTML which the browser doesn't have to figure out any more!). It still isn't quite 100% validating to the W3C spec (primarily due to old HTML in Webmin that the theme can't control), but it is getting much closer and will reach 100% compliance in a not-too-distant release (Webmin, too, will get some attention).

To get the new version on Red Hat, Fedora, and CentOS:

yum update wbt-virtual-server-theme

Or on SUSE systems:

yast install wbt-virtual-server-theme