Open the Visual Studio SDK command prompt. It's just like the regular Windows cmd.
Go to start ==> Programs ==> Microsoft Visual Studio 2005 ==> Visual Studio Tools ==> Visual Studio 2005 Command Prompt
When you get the prompt, type in clrver and hit enter. This should give you all the .Net versions running or installed on your computer. The clrver means Common language Runtime Version.
I hope it helps you.
- Proposed as answer by ZerdTwo Wednesday, December 08, 2010 9:23 AM
This article will show you how to check exact version of .net http://msdn.microsoft.com/en-us/kb/kb00318785.aspx