An HTPC (Home Theater PC) has many pros/cons over Tivo, but I believe that the long term cost/benefit of an HTPC is better than a Tivo. For instance Tivo's lifetime subscription is $400 the Tivo HD itself costs $200. Building an energy efficient HTPC initially costs the same but can skip commercials, take HD video where ever you want (online or off), is fully upgradeable, and can replace/consolidate your Blu-Ray and/or your DVD player. And you NEVER pay a subscription fee.
Things You Will Need
An HTPC Case (That accepts Micro ATX motherboards)
80 Plus (Bronze, Silver, or Gold) Power supply (unless included with case)
A Micro ATX motherboard with integrated video
2 to 4 gigs of RAM
500 meg SATA hard drive or larger
A DVD or Blu-Ray Drive
A low thermal power processor dual core or better
An Operating System (Win 7 shown here)
A TV tuner(s)
A 7/16 inch wrench
Connect your PC to your TV.