Well, it finally happened: weird things started happening, such as beach balls spinning forever and "force quit" not working; dock freezing; inability to shut down without unplugging the whole system. Ran "Applejack" and saw that the hard drive was failing: it attempted 10 times to repair, gave up and suggested Disk Warrior, then promptly shut down. Rebooted, heard the hard drive clicking and grinding, all fans screaming ... never made it to the log in screen (actually, couldn't get past the grey apple that precedes booting into OS X); rebooted into Safe mode (command-s) and saw a message that Journaling wasn't working, and something like, "sbin/start-up/failed, error 85". I could not boot into the Disk Warrior CD, wouldn't boot into anything. Looks like I'm going to have to reinstall OS X after I find another hard drive ...
So. looks like it's time for a new Hard Drive. The original hard drive is a 250 Gb Maxtor (SATA? ATA? can't remember ... whatever came in an original G5 2 Ghz Dualie (Rev A). My question is, where would be a good place to start shopping (on-line)?
Just checked Apple's web site and didn't see anything (I'm at work now and browsing around).