a. Insert XP CD in CD/DVD drive.
b. Reboot the system and change the boot order in the BIOS so that the first option is the CD/DVD drive. This will prevent the system from trying to boot your current XP install. Save the changes (hit F10), the system will reboot.
c. The XP CD will either boot automatically...more likely you will see some writing at the bottom of the screen that says "Hit any key to boot to CD". Hit any key.
d. CD will boot. The screens indicated on the link I previously provided for "Clean Install" will appear. When you get to screen showing your current install...delete it.
If that 8MB says "unallocated space", don't bother to delete it...if it says anything different, delete it also.
e. After this is done, your screen should reflect a total of 76xxx of unallocated space. The screen will present you with a number of options. You want to install XP on that total unallocated space.
Just follow the prompts and directions...have your XP key handy...have your drivers CD handy (will need this after install is complete and system boots new install for first time. You will again see the writing at bottom of screen which says something to the effect of "Hit any key to boot from CD" but this time you ignore it and the system will boot from your hard drive's new install.
The link for a clean install covers all this.