friend, u can format your harddrive by inserting the xp cd in cd-rom.after booting from cd-rom.it will give u option to format. then choose that and clean ur HD.if it not so send me message, i will give u another idea.
There are also DOS based Hard Drive wiping tools that actually write zeros to al the sectors. Formatting the drive does not assusre that data cannot re recovered from it afterward.
Killdisk is one of these DOS utilities.