^ dude, you can't delete windows from within windows... that would defy all reality, it would be like a snake being able to eat itself until it dissapeared (and if you're gonna say some shit about you said to use DOS, command prompt in windows is still IN windows)
So if you want to reinstall windows XP/2000, just pop the Windows CD in, reboot, and begin setup. In there there will be an option to format the partitions of your hard drive... just make sure you read every step carefully instead of just skimming through...(and if you don't want to install windows XP, just cancel out after you've deleted the partitions)(just so you know, with these steps, the drive hasn't been formatted yet, that's the very next step on the CD so you can do that if you want. You can't use a drive unless it's been formatted, basically it's just setting the drive up to be used)
If you use windows ME, 98, 95...
get a windows 98, ME or 95 bootdisk. (I prefer 98 boot disks... check www.bootdisk.com
for an easy place to get bootdisks)
pop the disk in, reboot.
type 'format c:' (or whatever drive you want to format, and wait...
although this way may seem easier... you can't use it with windows XP/2000, only windows 95,98,ME... that's because the older windows don't recognize the new file system (the way the drive has been formatted) of Windows XP/2000
hope this helps
Screw this I'm going skiing