You can't boot to the CD because of the way that Win8 shuts down. Simply put, on shut down, it puts itself in a state of hibernation, which allows it to boot quickly, but also prevents booting from another device on the initial boot.
The good news is, it doesn't do that on a reboot, so all you have to do is put the CD in the drive once Win8 is up, then do a reboot. Then the "Press any key . . ." should work.
You may get all kinds of error messages about "There's a newer OS", etc., when you go to reinstall XP. Please note that XP is not supported any more by Microsoft, and you'll have to install service pack 3 to get any security updates for it. You might be
better off explaining what problems you are having with Win8 now, and possibly the community can help you with them instead of rolling back to an extinct OS (don't get me wrong; I loved XP, and never even moved my desktop to Win7 until right before Win8 came
out).
If you don't like the new Win8 interface, there are ways to get around that, and make your PC look and act like Win7 or WinXP. Here's a pretty comprehensive list of third-party programs that'll do that for you:
<http://social.Technet.microsoft.com/Forums/en-US/w8itprogeneral/thread/b5f19449-f992-466b-b549-ce1452fd5a39#b5f19449-f992-466b-b549-ce1452fd5a39>
And my personal favorite method:
Ex7forW8 <http://forums.mydigitallife.info/threads/35189-Windows-7-explorer-for-Windows-8>
Start8 ($5) <http://www.stardock.com/products/start8/> and Classic Shell (free) <http://www.classicshell.net/> seem to be
two of the more popular ones.
I wish you luck with whatever you choose, but I would advise fixing and sticking with Win8 (I never thought I'd ever say that), if for nothing else than because sooner or later you're going to come across something you want that will refuse to run in WinXP.
SC Tom