As far as installing Tivonet goes there's a newbie guide
here that I found helpful. What I found especially noteworthy was the advice for installation on both the active and inactive partition. Tivo switches partition after an official SW upgrade and if there's a problem it will switch back to the old partition and keep running. By installing the software on both you retain functionality post-upgrade.
There's some additional tools on
pvrhack that you might want to play with, tivo-bin (IIRC) is a useful collection of linux tools you may find handy.
FWIW, I purposefully chose not to get listings via Tivonet and instead stay using the telephone line. My reasoning was that I couldn't see any appreciable gain doing it that way and for my troubles I'd need to ensure Tivo stayed hooked up to the web (in other words 'more to go wrong'!).