FreeBSD -current as of 20070302 now has the iwi(4) driver included in the base tree. But to use it one needs to define the legal tunable via loader.conf. I think Linux still needs you to download the firmware from Intel's iwi/ipw website. Wireless support for Intel PRO/Wireless 2200BG/2225BG/2915ABG now work out of the box.
[faith] ~> grep iwi /boot/loader.conf.local
# legal stuff for iwi