
So as you can see this is a case where my computer and the TV are already right next to each other in the room. Obviously that makes it a tad easier, sure, but this same application could be achieved by simply putting a tower next to that TV stand with no other hookups but say like a wireless mouse if you want to get the full effect of a "television"
although Windows Media Center thingy has a remote if I'm not mistaken.

It's hooked up with 1080i component cables, to which no I don't have that fancy of a graphics card. While it is an HD supported card, it only outs in S-Video, so they give you this nice converter to go with it.
Now what this does is allow me to view my computer as a second monitor in HD and thus, all I have to do is drag a player over and full screen it.
When it comes to things like "Apple TV" it's cheaper and ultimately more satisfying to hook it up the way I have it here (or with just a tower if it's in, say, your living room) to get the exact same effect.
Your computer is a DVD player, a Youtube browser, and a Media player all in one, plus it can play games, browse the web and so much more. All of this done on a HD flatscreen like mine and you're in business.