I finally got my FreeBSD laptop to authenticate to the company’s WAP 54G wireless access point. It turns out that the problem was with the Linksys firmware! I spent two days futzing with FreeBSD and trying to figure out why the iwi card wouldn’t associate with the access point, and finally in frustration I flashed the WAP54G’s firmware to version 3.04 (from version 2.08), even though the release notes said nothing about fixing WPA association. And it worked!
I guess this is what happens when you buy consumer-grade devices.