Thank you for all your feedback -- we have been working on improving the install experience under Vista as well as the design-time in Visual Studio 2008.
I am happy to let you know that we have addressed all reported issues and things are much better now. We are currently running thorough QA on the internal build and it will be available for download with the scheduled SP2 in the last week of February.
If any of you is willing to try the build even before the Service Pack release please send us a support message
All the best,
the Telerik team