Gertrude the wombat:
"Microsoft.net" was a marketing name for a set of concepts, now fallen into disuse.
The microsoft.net framework is very much alive and is still a core part of Windows 7.
The .net framework comes in many different flavours e.g.: -
Framework 1.1
Framework 2.0
Framework 3.0
Framework 3.5
Windows vista itself uses Framework 3.5 so other versions could be uninstalled from the Add/Remove programs without upsetting the operating system itself.
However any applications that require one of the previous frameworks you are uninstalling would then fail to operate as they require that framework to run.
Can you provide some examples of DLL names that are requesting administrative access as this could help in identifying what the problem is. By default the framework itself is not loaded until an application that requires the framework is loaded. The framework itself should not be asking for administrative access unless an application is requesting the framework to be doing something outside of the security zone the application is running in.
It may be worth going into task manager as soon as your machine has booted (Before starting anything)to check which processes are running - you may have a rogue bit of software such as spyware installed etc.
Cheers
Jof