This project has working code for the TI ACX100 chip which the DWL-520+ uses (and many other cards). Additionally, you will need the firmware off Dlink's ftp sever. I successfully downloaded the source code and compiled it on a Debian unstable box running a custom 2.4.22 kernel. The interface showed up as wlan0 and the tools from wireless-tools worked (iwconfig).
I've been dinking around with it for a couple of days and it seems I can't get it to host client cards (AP mode). I've tried iwconfig's "Ad-Hoc" and "Managed" wich no luck trying to get an iBook to connect. Trying to set "Master" mode failed with an error message. If I can't get it into an AP mode, back to Fry's it goes as this will need to work for my Node280.