My cheap 120GB 7200 rpm drive arrived today ($75) and I've put it in my empty external firewire enclosure.
Now I can psync my Mac OS X system onto it, rebuild the two internal 120GB drives into a mirror, and copy everything back.
Then I can disable the nightly psync across the drives (which is pretty lame).
Actually, my new drive is a little flakey (I was having trouble initializing it) but it seems to be working now that I'm having disk utility zero the drive while formatting it.
... while I've been waiting, I was drooling over iPods again. I think I'll spring for one after I re-roof my garage this summer.