Unless you have the Tivo with the built-in DVD burner, anything you do to rip content to your PC will void the warranty. If that doesn't bother you, read on.
Unless your model is an older "direct" Tivo unit, you can try using TivoToGo software (google search for it). If that doesn't work, you can remove the Tivo's hard drive and connect it to your PC via USB or IDE. The files will be in proprietary .tivo containers. To convert them, use
DirectShowDump.