If you are programming a web application for .NET Framework 3.0 or 3.5 you might be looking for the versions in IIS6 or IIS7. You ask where is ASP.NET3.0 or ASP.NET3.5 versions?

The right answer, there is NO ASP.NET3.0 or ASP.NET3.5.

This is what you see in IIS6:



This is what you see in IIS7:



There are 4 ASP.NET versions:
ASP.NET1.0
ASP.NET1.1
ASP.NET2.0
ASP.NET4.0

There are 6 .NET Framework versions so far:
.NET Framework 1.0
.NET Framework 1.1
.NET Framework 2.0
.NET Framework 3.0
.NET Framework 3.5
.NET Framework 4.0

.NET Framework 3.0 and .NET Framework 3.5 use ASP.NET2.0 runtime located at:
Code:
C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll
So, if your application is based on .NET Framework 3.0 or .NET Framework 3.5, make sure to enable ASP.NET2 in IIS6, IIS7 or Hosting Control panel.