For just outputting the desktop of your computer, you just need to have the correct connectors on each end (adapter(s)) if necessary, and it's best to have a graphics card that supports "tv out".
If you're connecting over HDMI, you shouldn't have much if any problems there.
As far as for "media center" type stuff, on Windows, you need Media Center or you need a 3rd party application, which there are a few of, but the names elude me at the moment.
If you want to try something different altogether, Linux MCE seems to be working pretty well now. And if you have other things you'd like to tinker with like a home automation system or home security system, it's DEFINITELY worth a look. It has lots of cool features. Now don't assume that it will work perfectly, like the videos try to tell. I've yet to see anything - regardless of OS - that is 100% bug-free through usage history.
There are some other Linux distros (free) that are for media center applications as well. Lots and lots of options, really.