I was able to uninstall Fedora Core 5 without using anything but the Fedora install CD and a WinXP CD. It worked like this:
First, boot from the first Fedora install CD. Follow the installation until you get to the partition screen
Delete all of the partitions you can. It will force you to create a root partition before you can continue with the install. Create it, then continue installing until it starts formatting the drive. Watch the indicator bar as the disk is formatted. As soon as it gets to 100% turn off the power to the machine.
Now turn the machine on long enough to put in a bootable Windows CD (I used XP). If necessary, turn the machine off and on again, and do whatever you need to to boot from the CD (usually F12 on Dell's).
At this point, XP setup should begin and will install normally.
Good luck.