my friend had the same problem knoppix has a VERY VERY hard time finding usb networking adapters if you can even get a driver for it which i doubt he ended up having to plug his computer into the router via ethernet cables and it had no problems at all. untill someone makes drivers for usb wireless adapters your gonna have to go wired.
or find something that works that he didnt (he looked around for weeks) didnt find anything

he tried using a Linksys wireless usb adapter