Recovering user files from hard drive with XP SP2

What would be the easiest way to recover user files (under Documents and Settings\<username> ) from a hard drive that I can't boot Windows from anymore?

What happened: My motherboard died (I think - won't even beep when trying to start it up, tried swapping out power supplies, no luck). I'd like to recover all my files from it, at least the ones that weren't backed up already.

What I tried:

(1) I hooked the hard drive up to another machine as a slave, but I'm not able to get at all the files that are stored under specific user profiles (since I'm not logged in as any of those users).
(2) I hooked the hard drive up to another machine as the primary (and only) drive, but that installation of Windows won't boot now. It gets to a certain point then just spontaneously reboots, whether I am booting normally or into any of the various safe modes. I'm not shocked that it won't boot because all the hardware (motherboard, processor, everything) is completely different on this other machine, but I figured I'd at least be able to boot in some mode & copy all the files I need onto a USB drive or something.

Apologies in advance if there's not enough info here to help solve my problem. Seems like this must be a common problem though so I'm hoping someone has a quick answer.

Hooking the drive up as a slave will allow you access to those files since the security isn't there from Windows.. try your slave drive set up again and it'll work.

Riser