I cleared out a lot of hard drive space and fsck'd it from single-user mode (didn't know the Command-S trick, thanks) (the filesystem checked fine -- no errors) and now it works like a champ.

I don't get it. It doesn't appear to be accessing the drive much at all now. Why would clearing drive space obviate the need for swapping activity? Maybe it was just horribly fragmented before. I'm still thinking about getting more memory for it, though.

Of course, I also need to replace the battery. It'll barely last 15 minutes now.