Before you start the installation you'll need to back up any
files that you want to keep from the XP Pro installation. Keep
in mind that installing XP Media Center will mean that you'll
have to reinstall any programs that you want to keep from your
current installation.
Once you've backed up all your important files you need to
configure your computer to boot from the CD. Once the
installation begins you'll be given the opportunity to format
the drive. Take a look at these articles for more info:
Courtesy of Michael Stevens, MS-MVP
Clean Install Windows XP
http://www.michaelstevenstech.com/cleanxpinstall.html
Clean Install Procedure with Illustrative Screen Captures
http://www.theeldergeek.com/xp_home_install_-_graphic.htm
Good luck
Nepatsfan
(e-mail address removed),