If also have Visual Studio 2008 installed on the same machine with VS 2010, and prefer to use the older toolset to target .NET 3.5, you can use the settings as follows:
Settings other than above are neither tested nor supported, and other settings may cause unexpected build errors or behavior. Even if the build itself succeeds, Microsoft does not guarantee that the specified C++ / .NET Framework version is actually loaded in the target application.
For other articles on configuration above, visit the PlatformToolset Property section of the following MSDN document:
MSBuild (Visual C++) Overview
Article ID: 2740044 - Last Review: 30 Aug 2012 - Revision: 1