Getting my series 2 tivo on the network was painless. I did run cat 5 cable and use tivo's recommended usb nic.
Another tivo enthusiast shares his frustration with setting up his series 2 with a wi-fi usb nic. He did succeed in the end.
UPDATE 30 AUG 2003
Tivo puts new wi-fi instructions up on their web site.
UPDATE 5 OCT 2005
If you are looking for wireless telephone extenders, which basically allows you to share your phone line without having to run a telephone cord along your living room floor, I found two models on Amazon that might work for you.
If you are searching for a usb based cat5 network adapter, I went with the Linksys model. Weakess has different USB ethernet adapters that are guaranteed to work with your tivo.