It took me this long, but I finally figured out that Rosetta@Home is far, far more memory-bound than Seti@home. Zombie 1, which has a Celeron @ 432 MHz and 123MB of RAM, had if I recall correctly an load average that was maybe 2 – 3. I suspended Rosetta, and what I had thought was the power light turned off. It was the hard drive light. The thing was eating swap like no other. I have to get more RAM in the poor thing. Zombie 4 was using swap too, although to a much lesser extent. It has a Pentium 3 @ 728 MHz and 124MB of RAM, so the CPU is a factor too. For now I’m going to detach Zombie 1 from Rosetta and start it back up on Seti@Home, where I don’t remember that happening. In the longer term, I’m probably going shopping for some RAM.
EDIT: Success. Load average is now 1.00.