I believe that Visual Studio is written in .NET.

I've been using it for several months at work, and I haven't had any problems with it.

I use Windows Vista, and have been doing so for about the past year. It has gotten better with time, (i.e. more stable etc.) If you have enough RAM, vista, in my mind, will be a good experience. More than just looking nicer, the integrated search is really nice. For me it is a big productivity enhancer. The OS feels a lot more secure, too. I like the UAC. (unlike many others) Vista does suffer from a perception problem, though. If that doesn't bother you, I recommend it.