well to format your harddrive, first make absolutely sure that you have everything you want backed up!!!
then its relatively simple, put your panther, or whatever disk in, and restart your computer then open up disk utility from the cd and from there you can format your harddrive, there are a few different options avalible, you can format it, zero out the drive or another, if you want to be really efficient zero out your drive and once you are done formating your drive then you have to reinstal the OS....
any more questions just ask! hope this helps