to use the DWL-G122 you have to compile the usb-drivers edition from SVN to get it to work.
The project moved a little while ago, due to new laws in Germany which make it illegal, and so the developer had to move. As far as I know everything is moved now, so you should be able to get the code and compile it.
Once you have it compiled, just copy it to your Applications folder and launch it.
Now it work nicely