Unfortunately installing separately the Telerik AJAX VS Extensions under VS 2008 is not supported. This is possible, however, under VS 2010 using Extension Manager deployment. See the bottom section of this blog post
for more details.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items.