Vague questions... Vague answers...
.NET framework is about to roll out version 4... so which version of the framework are open to using? Some companies for example limit to framework 2 for compatibility reasons.
And 'garbage collection' isn't as much a framework thing is a managed language thing: C# versus (unmanaged) C++
My advice is to go to Barnes & Noble (or your favorite book store or library), get a cuppa from their coffee bar and take up residence in one of their plushy chairs and start reading books. Get enough understanding of the things you are interested in to be able to direct your on-line research.
Of course, since its a Microsoft framework, that's a good place to start too.
Visual Studio page Google