Are you receiving any error messages from an application?
Windows 7 does come with .NET 3.0 installed (which can be activated/deactivated through Control Panel/"Turn Windows Features On or Off"). I believe though that all the previous functionality of older .NET versions such as 1.1 and 2.0 should be included in 3.0.
Unfortunately, some applications when they attempt to install or launch on your system are looking for a specific version to be installed. The application vendor might have a workaround as well for any such issue.
Hope this helps...
Mike
