I'm not you people.
(Please keep track of the user who you ask a question too).
When you installed windows 2000, (If you formatted the entire drive during install), you might have taken out the small partition that holds data for a system restore. No version of windows likes
you going backwards. In order for you're system restore CD's to work you'll need to format the hard disk drive. Windows will not install if Windows 2000 is found on the drive. The fastest way to get Windows 2000 off the drive without deleting any other partitions Compaq installed would be to go to the hard disk drives manufacture's site & download their setup tools/utilities. You'll be able to creat a bootable floppy disk that will function in a dos-like mode out side of windows. You'll be able to format the Windows 2000 partition. Once that is done you will be able to incert the restore CD (s) & install Compaqs windows XP.
You may need to pull the drive in order to see who made the drive. EX; Seagate, Smsung, Maxtor ect. Here is the link for Seagate. http://www.seagate.com/www/en-us/support/downloads/seatools
Every manufacture has similar bootable floppy software.
Read the instruction provided by the manufacture on how to create the floppy disk & how to run it.