Not all 802.11G cards work the same, and there are different levels of WPA encryption that figure into the equation as well.
For instance, with the WCF54G on my 900C it would only connect in "B" mode.
With the Ambicom WL54-CF card, I could only get it to work if I used the Cmonex flash. She must have loaded some driver support for the card in her build. It would work with my home Netgear router using WPA-PSK security, but not WPA2.
Using the Samsung MagicLan SWL-2610c, I was able to connect to any G-band router, but only if it used WEP. If the router used WPA at all, I didn't connect.
Lastly, using a USB wifi is a hit and miss thing as well. My RT3070 stick works okay on my CE5 and CE6 devices in "G" mode, actually it works okay in "N" mode as well...but only on some devices.
My USR MaxG works okay on some of my CE5 or CE6 devices that support RNDIS, and it supported WPA-PSK and WPA2 protocols on at least one CE6 device.
Chris wrote a great CESD on it here:
http://www.hpcfactor.com/support/cesd/h/0029.asp