I'm about to partition my hard drive. How many gigs should I allow for my XP which is and will be my master O/S. I have all my programs, files, and folders on it and will be copying them to another partition for safekeeping, but will only be moving high volume files like audio, video and photos? I won't be adding anymore large programs or files, so I would like to give it a 30 to 50% buffer to be safe. If I add up presently used space on my C and D drives and then added my buffer would that be correct? Do I need to calculate the space the files I'm moving and subtract that? Is there a formula or rule of thumb to use?