I faced a problem today where the XAML Intellisense was broken inside the XAML Browser in VS 2008. I researched a bit on the internet and found the following link that helped me solve the problem. The problem appears when you install the Windows SDK after you have installed VS 2008.
Here is the link: Installing Win SDK after VS2008 breaks XAML Intellisense
Hope this helps,
Regards
Tags: VS 2008, WPF, XAML