Only the GUI (Graphical User Interface) is .NET. The rest is C/C++.
If you are having trouble with .NET, then it seems likely that your Windows install is either misconfigured or defective (perhaps by a previous software installation). Users have problems with all types of software, even games, and installs of seemingly harmless apps can cause major problems for some users. Don't blame .NET for any bad experience. I've still to see any PC that has had issues with .NET installation, so its pretty rare (win2k/xp only, I can't speak for users of win98/ME systems).
And yes the new drivers still have some bugs to iron out, but that will happen in time. Bugs are expected whenever new software is released.
You can tell if .NET is installed because you'll find it mentioned under [Control Panel > Administrative Tools > Microsoft .NET Framework 1.1]