This has allowed me to connect to my AirPort Express router. It feels great making an 802.11g connection with a machine that is deemed not AirPort Extreme Ready.
Of course, I want to secure my network. I can set up my Base Station using the AirPort Assistant, but how do I setup the adapter correspondingly? AirPort software only works with the original unobtainable AirPort card. After I tried everything else, I read the manual. Go to System Preferences » Network » Configure and switch to manual IPv4 (or set it up as a new location). Type 192.168.2.220 for the IP address, etc. Follow the instructions in the manual which are intended for Windows. Use the reset buttons on your Base Station and adapter in case things do not work out; even unplugging the USB may be required. Success!
[robg adds: Note that this is not really a portable solution in terms of size; it's more like a typical wireless router, not a cardbus solution.]

