I have not had time to work on this to much yet, BUT. My boss said it works fine in IE7.
I use IE8 on windows 7 and just found out I can use IE8 to render IE7 by doing this inside Internet Explorer 8 (as the 7 rendering engine is bundled with 8)
1) Open IE8
2) Open >Tools >Developer Tools
3) Switch Browser Mode to IE7 and Document Mode to IE7
After doing this the Artisteer skins render fine in mojoPortal with Telerik controls.
So, The newer IE8 and FF 3.6.8 show the problem.
With IE7 rendering ok now, this will hopefully help me compare the markup from IE7 to IE8 and narrow the problem down.
More on this later...