Is it possible to connect to 2010 TFS from Visual Studio 2008 Professional
There is an update VS90SP1-KB974558-x86.exe that is targeting VS2008 client, but that update did not recognize Professional version of VS2008.
Although TFS2010 is part of professional MSDN subscription
This blog post should get you going.
Quoted from post:
The order is important and you have to enter the full URL in 08.