How do I uninstall Windows XP? I have a F DISC.

First make sure you have a starting disk with basic OP (for instance XP or 98) on it.
Than type format c:/u to delete all windows data and all other data from that drive (if c is the drive with windows)
If you have more than one OP on the computer in different drives, do not format c , as all data how to reach other OP's will be erased than as well.

If you want to install any other OP on c do as above, and afterwards restart the computer with the OP CD in the CD drive.

Note : just the "format c: "command will not delete all windows files.

No necessary to delete Windows XP
Just Run Windows XP Bootable CD... from this it will ask to format the disk

Can you explain WHY you want to do this. Its not a usual step.