I am trying to format c: and erase everything on

You can boot from your windows xp disk. Just put it in the cd rom and while booting up press del or the key your boot screen tells you to enter bios setup. then select your first boot device as cd rom.

When installing windows xp you will have the option to delete your c drive and create a new partition in its place.

Hope it helps.

You can't format the drive while Windows is running. Insert the CD, reboot, and follow the prompts to delete and re-add the main partition, then do a Quick format.