Set your bios to boot to the CD. Put your XP disk in the drive.
Boot into the Windows XP installer. Delete the partion. You can re-create it and install XP or don't do anything and let whatever OS you intend to install do the creation for you.
Half the time that doesn't really delete the partition and you get 2 installations of the OS.
Been there, done that numerous times.
An FDISK floppy will utterly, absolutely "nuke" it....:)