I decided to take Adrienne’s suggestion and install Akismet. That required me to upgrade from WP version 1.5 to 2.0.whatever. A couple hours later, it looks like everything is running smoothly. (It shouldn’t have taken that long; chalk it up to my stupidity, the stupidity of the FTP client on Windows 98 [why am I using Windows 98? the department I'm working for can't afford a new computer, and my laptop can't connect to the network at work], and a little bit of stupidity on the part of the one-click installer at Dreamhost [I originally installed WP to one directory, then moved it, but the installer thought it was still at the old directory despite the fact that that directory was empty... that was bad].)
Please let me know if anything has become broken. Now that I’ve installed Akismet, comments should show up right away again.