Thanks! These essays are certainly enlightening. My computer already has UEFI installed, and I don't want to convert it. But I now have a better idea of what's going on down there, and what to be careful of. My idea of using a second hard drive seems better by the minute.
I suspect that part of my problem might have been the installer for PC-BSD. That's the FreeBSD variant I use, and I apologize to all the purists in the room. [grin] In short, if you select any disc install option different from the default, it fails to install. But the last time I installed it (on the aforementioned Dimension box), when I gave PC-BSD it's own hard drive, everything went fine.
The fact that the Dimension suffered a mobo failure about two weeks later wasn't PC-BSD's fault. Or Windows XP's for that matter.
Anyway, what I want to do is something akin to what this guy did with Ubuntu Linux:
http://www.linuxbsdos.com/2012/11/05...fi-hardware/2/
(I hope that link works.)
I would put the FreeBSD loader in the boot sector of the second hard drive, then use the Windows 8 boot loader in a relay, like this guy did. I understand that other users have done similar things with Grub.
The research continues...