I would probably just get the cheapest one from OWC, such as the $15.99 Newer Tech one. But you are probably better off not spending any more money into that machine. I would use ethernet if you can arrange the wiring as USB 1.1 is very slow (1.5 Mbps max).
I found a new USB card at a local shop and put it in. Here's hoping all will work! Ethernet is not an option- this is set up in my studio, which is at the back of the property and doesn't have phone hookups.