Here's the deal with Tivo's.
ALL models can fast forward through commercials. No Tivo does this automatically, you can turn on a "30 sec skip" feature that rocks.
You must pay the lifetime subscription ($299) or monthly ($13) to use the Tivo. Without it, all you can do is pause live TV. For a while, Series 1 Tivos could be used like a VCR without a sub, but they upgraded the software to prevent that. The only exception is models with Tivo Basic - then it can be used like a VCR and has a 3 day guide (Tivo Plus has 14 days and you pay lifetime/monthly). There's a (discontinued) Toshiba Tivo with a DVD player that has Tivo basic, otherwise any of the DVDR's with Tivo (other than the Humax) have it too.
Lifetime subscription is for the Tivo's lifetime, not yours. This lead into my next point.
You want the newest model Tivo you can find. The Series 1's (all black, made by Phillips usually, some silver ones made by Sony) had modem problems and were of shoddy quality. They don't support broadband without some extra modding. They're louder and larger.
Series 2 support broadband with the use of a USB network adapter. They're a dark grey color.
Series 2.5's are just like Series 2, only they're a lighter shade of gray with a two-tone "faceplate". These are the newest models.