Gunlok

I bought OEM XP pro to install over W2K. Somehow I've ended up with both OS on the drives. Maybe when it gave me an option to install over the existing OS (option L), I missed it. I'm not sure. W2K doesn' respond, and I can't get to any options that will allow me to reformat the drive and start over. Even when I try a new install of Xp, the option to delete Partition C will say "unable to perform this function due to needed files being present'. How do I wipe this drive clean and start over??