Hi,
If you DO NOT want to keep any data on your computer (ie. wipe it completely - ensure you backup any data off the hard disk before carrying this out!!), you can do the following:
Put the Windows XP Pro CD in the drive and turn on the computer,
Boot from the CD
The WIndows XP setup will begin
Choose to delete any existing partition's
Create a brand new partition using the maximum amount of disk space
Choose to format the partition (NTFS - quick)
Now install windows to the new partition, following the onscreen instructions.
This will remove the existing 2000 and XP installations, and create a new XP installation.
Hope this helps!
- BigThunder