really the only difference is cost and time/ effort.
TV is very low resolution and additionally both depend on your bandwidth.
What it boils down to is; Do you have a screwdriver and are unafraid of cracking your PC's case open? With the time put in, it will give you far better results than any commercial solution. I'm personally running ORB, Hauppauge TV tuner, a cheap NVidia 256Mb video card with a 16Mb sound card on a 1 Ghz Athlon. From the demo units I've seen of slingbox, I wasn't too impressed.
The Slingbox, however, is a quick no fuss solution with easy to use software. Pricier but geared towards the guy that'd pay $60 for an oil change on his PC