How can you re-install a file system to a hard drive without formatting it?

I’ve got a 1TB external HD and after copying some corrupt files to it the whole thing is a bit knackered. The FAT32 file system no longer shows which I’m guessing is why Windows thinks it has 0 bytes of a capacity of 0 bytes. Is there anyway of getting back the FAT32 file system without formatting the drive? I really don’t want to lose the data and I have been quoted a price of £100 for data recovery, plus the cost of a new Hard Drive if needed. Obviously if all they are going to do is something I could do with the help of fluther I would rather keep my £100.

I’m using Windows XP sp3