So you now have a drive with no OS on it, or anything else like data or a recovery partition you need to keep?
You installed Windows on the same partition as an earlier install, then decided to delete that same partition?
But if you want to clean the drive, you can use Diskpart. Boot to the Install DVD and on the first screen hit Shift+F10. Then type Diskpart and wait for it to stop. Then look for and select the drive you want form the disk list. This will clean everything off the drive, so if you have something you want to keep, you need to use some method to move it.
Diskpart
list disk
select disk 0 <-- make sure correct disk is chosen from list
clean
exit
exit