First thing you will want to do is use ifconfig -a to show all the interfaces. You might see ra0 which if I remember correctly the DWL-G122 uses the ralink chipset. If you don't see it then you will have to compile the driver yourself.
unzip and untar the package.
the cd into the correct directories. You should see two make files. one is makefile.6 and the other is makefile.4 These are for the different kernel versions. Use .6 if you have a 2.6 or .4 for 2.4 kernel. you will have to do a
cp makefile.6 or .4 ./Makefile
then just run
I think you will also have to make a Path under etc with the following two folders.
/etc/Wireless then /etc/Wireless/RT2571STA or RT2500STA or RT2700STA then copy all of the .bin files from the directory where you made the modules for the Dlink. I believe the the install document is pretty straightforward.