We have more than a few StinkPads around and they seem to work pretty well with the card. Some use WZC, some use PROSet, and some use Access Connections (all machines run XP SP2/3 or Vista). If you've already checked the drivers and card settings (xmit power, etc.), then about the only things I can think of are: check the antenna connections to the card (which might not be easy to get to), and you might also check to make sure that the laptop's BIOS/chipset can't play around with the NICs power settings. Try disabling all the BIOS and OS power saving settings and see what happens (you could also see how the card performs when the laptop has AC power attached versus running on battery).
I recall seeing a new, very small, Dell (D4xx?) that we ended up giving a CB21 due to the built-in card's inability to maintain a connection, but I'm not sure what NIC it was using (it was definitely an Intel 3945 or 4965). I did not have time to diagnose that laptop and had to punt it to the desktop support folks, but I personally updated the driver and checked the configuration before running out of time.