My guess is you've got a lot of garbage left over from the Win7 install. Dump files, swap files, crap like that. If you run a disk cleanup, my guess is you'll get a pretty large chunk of space back. Keep in mind that you are never going to get those numbers to match on a system drive (they should match pretty closely on non-system disks, or if you check a system disk that's not being used as a system disk currently)and quickly added in my head all the bits of data and came up with 30-35gb's which is what I expected, but when I go into my computer with all my drives drive C says 196gb.