I am trying to install Windows XP, but prior to doing so, want to get rid of the current operating system I have, namely Windows 2000 running on NT Service Pack 4. I am struggling to format the disk.

Any help much appreciated!

are you formatting it from the xp cd (by following the options to perform a clean install)? if not, trythat
if you are, what error message are you getting?
here is a good guide for a clean install: http://www.michaelstevenstech.com/cleanxpinstall.html

Hope this helps
Mike