You don't by any chance have a Belkin USB Wireless Network Adapter handy do you? I have one of these and managed to find software which lets me use it with a MacMini (running Mac OS X 10.4.7). I could have sent you the software to try it and, if successful, you could use that adapter with the Mac and bought another to replace it.
The reason I suggest trying it first is that there appear to be different versions of Belkin's adapter, although they look identical. Email me via the yellow envelope if you want the software.