If you want to go from Windows 7 down to XP, the only option is to perform a fresh clean install. Put the XP CD in the CD-ROM, restart the computer. You have to make sure that your Computer BIOS has the CD-ROM as first priority in the boot order. If it is, the system will prompt you, shortly after the POST, to "Press any key to boot from CD". Then follow the prompts during the installation of XP.
When you say "I plan to", that's fine. but the answers to the following would be handy;
why? is it a 'my computer is slow on W7', or 'I know and therefore prefer XP', or something else.
Just a thought, tech keeps moving right along. Official support for the XP platform is due to expire soon. Windows updates, support patches, etc are all due to stop.
Do you have an instllation meduim for WXP? eg installation disk, etc?
3.Do you have a Lic code for the same version of XP (either Home or pro) - else the install will fail, usually.
are you sure that you can get driver support for XP for the computer you want to downgrade? many new PC's don't even support XP at all.
is this your only computer? if all else fails, can you get W7 back on it?
If you do go ahead, please make sure you get all the drivers for your new OS first, ESPECIALLY the networking ones, so you can get back online with the computer.
Do you need to back up W7, do you have personal file on it, or was it a clean install?