I can find no reference to the DWL-G122 being compatible with OS X or with any flavor of Mac. If it is, then it is the only one out there and is sure to be in great demand.
I think you are out of luck on this one.
Question: Is the adapter recognized by the iBook and does it appear in the Network Settings Pane of System preferences?
Question: Does the Airport Setup assistant recognize it?
Question: Did you buy this directly on line or from a store. If from a Store, did you tell them what it was for and how is their returns policy? If on-line, what prompted the choice of DLink.
I, and hundreds of others, have been searching for a USB adapter that will work with Macs. So far I have found one, Farralon, but this is no longer made.
For the iBook G3 you will need the Apple Airport card, NOT the Extreme one, which is no longer made by Apple. It is available on the web at prices ranging from $50 to $150. It works on 802.11b which is the slower speed wireless standard.