Strange behavior when installing 2nd OS

Here's the scenerio: Windows 7 7100RC is installed on my custom PC. I wanted it to dual boot XP Pro x64. I shrunk the Win 7 volume to be able to create a partition for XP. Everything's good so far.

I insert the XP Pro x64 disk and reboot. XP begins to load. The install gets all the way to the point where it asks about where to install it. I indicate the new unformated partition I made. I tell setup to format the new partiton, then all of the sudden, the computer shuts off - dead. It does not reboot!!!

Confused, and remembering that Vista doesn't install on more than 4gb ram, I remove half the ram in the system from 8gb to 4 gb.

I then retry to install XP Pro x64. This time I only get to the partition listing before it shuts off.

I then power it back on and let Windows 7 load, the boot loader hadn't yet been damaged from XP. It is stable...and its been on now for roughly 25 minutes. So I know that no hardware is shorting or being defective.

What is going on here?

More info: Googled my issue.
* Hard drive is not bad - drive is brand new, had it for less than a day, and runs win 7 fine (even after having been cloned from a previous older drive)
* RAM - if any was bad, then I'd have problems with win 7
* Mobo - maybe a month old, and works correctly or I would have problems with win 7
* Install disc - is a burned copy, probably the cause, but not sure why it would work all the way up to said point.

You have to install xp first and then win7. Always go old OS to new OS.

I havn't done a duel boot with win7 and linux yet, u should do some research on the flavor ur gonna install and make sure the bootloader works with win7

If you really want to get xp on ur comp u can read this.
Windows Vista no longer starts after you install an earlier version of the Windows operating system in a dual-boot configuration