I know that .NET Framework is not backward compatible (ex. Installing 4.0 dlls does not include 3.0 dlls)
But what about Windows installations? ex. Windows 7 includes .NET 3.5, what about 2.0 is it installed as well ?
Which Windows versions includes .NET 2.0 dlls?
.NET 3.5 does include .NET 2.0 DLLs. It is the same CLR. See here for an overview:
http://blogs.msdn.com/b/astebner/archive/2007/03/14/mailbag-what-version-of-the-net-framework-is-included-in-what-version-of-the-os.aspx