This sounds like a very difficult task but its really now.
Lets take it a scenario to make it happen .
I have a Widows 2008 server with IIS 6.1 installed on it . I have some applications running on it already which are built on .net2.0 framework.
I want to host new application built in .net 3.5 or 4.0 framework .
- Download the new framework from below link
2. install it .
3. Restart computer
4.now register the new framework on IIS server
5. Now you will get new framework application pool in your IIS
6. Assign this application to your application.