Had a very interesting experience trying to format an internal hard drive under Windows 7. This is a hard drive that was running Windows XP and then got corrupted. Rather than do a repair, I bought another internal drive and loaded Windows 7 on it. I then installed the old corrupted hard drive but every time I tried to format it, I would get a message that the drive was in use. The solution I came up with was to take it out, put it in a external enclosure and format it after plugging it into my laptop wihich is running XP. If I plugged it into the computer running Windows 7, I got the same "in use" message. I am guessing that Windows 7 was somehow recognizing and opening some of the OS files on the drive. After reinstalling the formatted drive it was initially not recognized by Windows 7 but I went into the Disk Management and activated the drive (right click on the icon to the left) and now its fine.