Unfortunately, Visual Studio does not prompt you for the SCC to use (at least, I could find it). So I wrote a little utility that plays with the registry and lets you set a specific SCC as the default one.
Application to Switch Version Control Systems
I have to use 2 different Source Code Controls: Microsoft Visual Source Safe and Rational ClearCase. Both of them provide a nice integration with the Microsoft Visual Studio IDE, so that I can checkout/checkin files while editing them.