if your hard drive has a partition (recomended) you can sore what you would like to save on the one side of the partition, then format the side with your o/s on it.
if you don't got a partition you stuffed!
although you can download a programme called partitiuon magic. with this you can make a partition on your existing hard drive. then place keepers on one side and re format other.
woz
woz