I have recently spoken to a number of people who were under the impression that older versions of Visual Studio could not connect to TFS2010. This is not the case. So for example you do not need to keep a TFS2005 running for your VS2005 clients.
Why you might ask does this question even come up? VS2010 can build any .NET 2.0 –> 4.0 project so why not upgrade all your projects to VS2010? The answer is that products such as Biztalk and SQL Business Intelligence use older versions of the Visual Studio Shell e.g. so for SQL 2008 BI you are using in effect VS/Team Explorer 2008. Though it must be said this issue is getting better currently a BI developer still ends up having to use VS 2008 (until SSDT arrives with SQL 2012)
Also some companies may just have a policy to stay on a version of VS for their own reasons.
Either way this is not a barrier to using TFS 2010. The key to getting these older versions of Visual Studio to talk to TFS2010 is only a matter of applying the correct patch sets, so for
All the products can be installed side by side.
Another point to note is that if you are using any of the TFS 2010 PowerTools and want the same features in old versions of Team Explorer you must also install the 2005 and/or 2008 PowerTools versions. Even if the 2010 PowerTools are installed, they will not be found by the 2005 or 2008 clients. The most common time you see this issue is when using check in policies.
For those of you working with VS2003 or VB6 all is not lost, you too can use TFS 2010, you just need Team explorer 2010 installed and the MSSCCI provider
Hope this post clears up a bit of confusion.