Endless restart loop - and cannot boot into Safe Mode

The computer is a friend's Advent DHE X22 running Windows XP Media Center
Edition 2006. The PC is caught in a never ending restart loop.

At switch on the computer confirms that it could not start up properly at
the last attempt to boot - with the usual screen suggesting that I can
start in 'Safe Mode', 'Safe Mode with Networking' etc. My intention was to
boot into safe mode and disable automatic restarts to try to troubleshoot
the problem. But selecting any of the options available from 'Safe Mode' to
'Start Windows Normally' simply repeats the cycle of restarts.

The only Windows disk available at the moment (until he finds his recovery
disk) is my own standard Windows XP Home SP2 disk. When I turned on the
computer with the Windows Home disk inserted, I was able to start the "boot
from CD" process, progressing to the stage at which it asks whether I would
like to re-install Windows etc. At this stage the computer does not reboot
itself, indicating (I think) that the problem is not hardware related, but
probably driver or registry related.

I stopped at that point as I'm not sure of the consequences in trying the
Windows Home 'repair install' routine on a Media Centre PC. Is there any way
I can get the computer to start in Safe Mode so that I can at least start
the trouble-shooting process without a Windows Media Center Disk or the
original recovery disk?

--
Falcon:
fide, sed cui vide. (L)