<p>How do you generate C# classes for accessing WMI?</p>

To generate strongly typed WMI classes, use the Management Strongly typed class generator (MgmtClassGen.exe).  It's usually in C:\Program Files\Microsoft Visual Studio X\SDK\vX\Bin.  The parameters are
at MSDN
and they even have
a page
describing the code generated.  If you have to do a lot of work with WMI, it's a lifesaver.