You can just install whatever flavour of windows on any unpartitioned space you have. If you dont have any unpartitioned space remaining on your hdd, then you must use a tool like partition magic to create a partition. You format the partition with fat32 if your installing 98 on it, or ntfs or fat32 if your installing 2000 on it. Im guessing the partition windows xp is installed on is ntfs, if this is the case and your installing windows 98 on the spare one, then to be able to see the partition from windows xp, you need to have both volumes formatted with fat32. Its just a simple matter of popping in the cd, booting from it then during the install selecting the partition you want to install it on.