And if you wish to erase the full drive, remember you cannot erase a drive you are booted from. This will mean either the internal drive will need to go into an external caddy and do it that way, or if you have the install disc which came with the computer, you can boot from that by holding down 'C' immediately after the chime, leave the Installer, go to Utilities in the Menu Bar, select Disk Utility and erase disk.
Format Mac OS X Extended if it is to have OS X instaklled at any time, go into Partition and under Option select Apple partition Map.