I only have a 20gb hd as my C drive, but I still have 6gb left, becasue I have other smaller hd's with most of my games on them. As for cleaning your hd up, just try and move stuff to other drives, or back stuff up to DVD/CD's if possible, hell it couldn't hurt. As for defragging, it certain;y can't hurt. As you use programs, move files around on your drive, and add and remove programs and files, sometimes the file clusterscan get scattered around the drive, because it just moves them around to suit itself as best it see fit to do so when trying to access information on the drive. Using the defrag program, it tries to put all parts of the files back where they were set to go; well it basicly organizes your hard drive so that it doesn't have to look all over the drive for all the parts of a file. When files get too fragmented, they take longer to load, which eats up system resources.