Can you see the harddisk in the BIOS?
Also, the system not recognize your Win XP as valid, what do you mean with that? Can't you boot on the CD or what is wrong? Did you buy an OEM version and have installed it on more then one computer? That is a no-go, you need a retail version for that if you want to stay legal.
seeing as i bought this a month ago and was ok on my other computers.
Sorry, but I can't see your computer. What is this 'this' you talk about?
If the harddisk can be seen in the BIOS all you have to do is download Delpart from here:
http://www.russelltexas.com/delpart.htm
Place delpart.exe on a basic bootfloppy (on WinXP format a floppy choosing to make a win98 bootdisk) or download a Win98SE or WinME bootfloppy image from here: http://www.bootdisk.com/ run the image and copy delpart.exe to the floppy. Then boot on the floppy and at A:\ > write Delpart, hit Enter and follow the onscreen instructions.
WARNING: Make sure only the harddisk you need getting deleted is physically connected to the motherboard as the program DELETES ALL CONTENTS ON ALL HARDDISKS IT FINDS.