a slingbox: you run your coax, rcas, or hd signal to the box and you also run your internet cable to it. It broadcasts whatever is on (and you can change channels remotely through the slingbox) through an FTP, basically your own personal website it sets up. Anywhere you are on your PDA, cell phone, laptop, desktop and have access to the internet you can watch/record tv
a tuner: usb or internal for desktops, you can plug your coax into it or antenna into it, watch and record tv.
Both are neat to have. Circuit city and best buy and newegg.com all sell these.