I believe that if you install the 3.5 framework, you will get everything back to environment 2.0. Structure 3.5 (and 3.0) runs in the CLR 2.0 environment, so you really get version 2.0 with the additional goodness of 3.0 and 2.5 on top of it.
1.1.
: C:\Windows\Microsoft.NET\Framework