Windows Media Center PC's normally Have a TV Tuner in them.
I am running a Windows XP Media Center Edition 2005 system, and the only bonus's that I can find is the Media Center (Can watch DVD's, TV, Listen to music, all in the Media Center program, You can also hook it up to your xbox 360, which I love becuase I can stream TV to my room (no outlet). It comes with SP2 integrated into it, which most PC's do nowadays. It also comes with "Digital Media Enhancements," Which is just some crappy dancers and an audio converter.
It looks much nicer too
Thats about it. If you want a TV tuner, go for a Media Center. The graphics card isnt normally powerful (usually something like a X1300), so I would suggest upgrading it to at least a X800 XL (even though the model number is lower and the card is a bit older, it still kicks the crap out of a X1300 by about 1300x :P )

I would say wait and build your own computer with a Intel Core2Duo E6700, if you can get your hands on that piece of amazing hardware by intel. It kicks the CRAP out of the best AMD cpu, and is less than half the price.

Or you could send the money to me and i'll "build" you a computer :P:P

__________________