a full format will erase the data
a quick format will only clear the allocation tables.
choose full format NTFS.
if you just want to format and reinstall your OS (M$ XP), just throw the cd in during start up and make sure you boot from disk then follow your nose from there.
Data can still be recovered after a full format. To wipe it completely use a program above or "DOD wipe". These utilities write and rewrite info over all the orginial data multiple times so it can't be recovered. Some of these untilities will do the same thing for your "recycle bin" and will actually erase the data in the same manner when you empty it.