How did U try to format it? With some utility? At the windows setup screen by booting from xp cd?
U can try by recovery console :
Boot from xp cd, press r (recovery console) , press win instalation(usually 1), press enter
Type password if U have one, if not just press enter.
format x: /q
replace x with the drive you want to format
q means quick
U also have more options like the type of file system to use
example to use ntfs type
format x: FS:NTFS /q