The smart card in a DirecTV box is comparable to the SIM card in a GSM phone. The card implements the personalization necessary to decrypt the shows that you pay for that your neighbor doesn't.

Before you shell out your money, make sure you know what DirecTV will charge you to set up an account like this. They're hesistant to mail out new cards, since those can also be raw material for people who don't like to pay for their TV. Likewise, check out the prices for new gear. I got my gear from American Satellite a couple years ago. They shipped it to me, and a third-party installer showed up to make it all work.

Right now, they're charging $200-$260, depending on which TiVo model you want to get and which dish you want to put on your roof. I have a Series-1 DirecTiVo, and I'd strongly recommend getting one of the Series-2 units if you can. They're smaller, quieter, and may eventually support the TiVo Home Media Center option via the USB port.