if you are able to boot from your floppy i would say get a MSDOS boot disk with that you chould be able to get to a command promt and use Fdisk to delete the partitions and remake one to use for new install, also note if you use fdisk to delete and remake partitions you need to do a format c: at the prompt so you can use the partition also the windows xp installer should have a format system with it if you can boot from that install cd you can delete the partitions from there as well when you choose what partition you want there should be an option to delete them as well.
i hope this information is helpful.