Thanks to everyone for your help.
Since my computer's from my university, I called up their tech support yesterday on the off chance that I was still covered (I graduated in May, so I assumed my tech support coverage had run out). Turns out yesterday was the last day of coverage, what luck!
Anyway, the problem is apparently one that many ThinkPad R40s and T40s have, and it has to do with a driver needed for Think Vantage Access Connections, the default LAN management program. I uninstalled that program about a year ago, because it was giving me serious trouble and making my computer run extremely slow.
Basically, there is no way to fix the problem unless I reinstall Think Vantage Access Connections with the new driver, which I'm not too keen on. IBM doesn't support any kind of fix if you're using windows to configure your wireless connection. On the upshot, the guy said that the IBM program is now much better and doesn't slow down your computer as much, so I'm at least going to give it a shot.
Thanks again everybody--at least if this same thing comes up again, you'll all look like geniuses for knowing the answer