well, push F2 or delete to enter your bios.Your looking for boot order, It will either be under boot options or in the award bioses its the second option down. Change the boot order so that ATAPI CD rom is first boot device. Put in your Windows XP disk. The installer will load. You will see a few partitions, push d (i think, it will say) to remove them and L to confirm you want to delete it. Then push enter on the free space and it will automagically create a new partition and ask you what you want to format it as, either NTFS or FAT32. Either is good, if you need to encrypt your data choose NTFS. The rest of the XP install is pretty straight forward.
BACK UP YOUR DATA YOU WILL LOSE ALL OF IT