Apparently I forgot to RTFM. If I had, I would have realized that FreeBSD can only be installed on a primary partition, and not a logical one. No offense to the BSD fans out there, but that is just effing lame (as is the installer itself - good grief). Very MS like, if you ask me.
Well, anyway, I still have my 12GB laying around inside the case without a power cable. Maybe I'll just fire that up instead.