* An upgraded CPU - the aspect of this whole operation that took the longest and the most swear words to accomplish,
* The rEFIt boot menu and toolkit,
* A Debian net install (my preferred distribution for this kind of a use) via unetbootin,
* A couple of resistors in a DVI to VGA adapter to fake the machine into believing it has a monitor attached,
And voila! I've got a headless Mac mini to replace the aging Linksys NSLU2 that has served well for many years.
Thanks Internet for the help and suggestions. Next up, adding some more disk space and turning it into a host for more household backups.