You could always use a program that comes from MS called diruse.exe. You can find the download at
http://www.microsoft.com/windows2000...g/diruse-o.asp. Install this to c:\windows (that's how I do it anyway). An example of running it is:
Start->Run: cmd (get to a command prompt)
cd \
diruse /m /* .\
From there, you can "cd [dirnamehere]" and run the same command again to find out what subfolder uses the most space.