Comment 1 for bug 342261

Maybe this is related to poor performance caused by layered windows (allowsTransparency = true) on win XP being software rendered and not hardware accelerated
http://social.expression.microsoft.com/Forums/en-US/wpf/thread/5c795519-a642-4a7d-9f5f-a029168e5225/
hotfix: http://support.microsoft.com/kb/937106/en-us