I was trying to get a Linksys WMP54G card going (another thread on the forum) but had also purchased a Belkin Wireless G Plus Desktop Card (F5D7001) as a backup plan. Thanks to Posmanet, this is now working for me. Seems that 'rmmod bcm43xxx' is the trick.

Before that I tried using the "firmware cutter" (bcm43xxx-fwcutter) to extract firmware modules. Limited but no ultimate success with that approach. Used .inf and .sys files found through the ndiswrapper wiki. Specifically...

http://biginoz.free.fr/linux/bcmwl5a.inf
http://biginoz.free.fr/linux/bcmwl5.sys

Haven't tried to duplicate and automate this setup so we'll see if it sticks. Also would like to see if I can get the bitrate over 18Mb/s.