Here's some info I found...

"I picked up a Dlink DWL-122 USB 802.11b adapter about two weeks ago, works just fine. It is one of the only USB wireless adapters that I could find that has driver support for Mac OS X."

http://www.macosxhints.com/article.php?story=20050201091946184

Then there are also Ethernet to Wifi adapters which should work but cost more.

Bruno