UPnP TV Server??

I'm not sure what you're after but, there are a couple of appliances that tap into your computer if you have Media Center.

Something else you can do is to put 1 or 2 tv tuners into your pc, and use either snapstream 4 and its streaming content add-on or if you feel comfortable enough with linux, you can use myth tv or knopmyth. Knopmyth is a livecd so you don't have to install any linux on your pc. Myth has a front end back end arrangement where you can have 1 or more servers and 1 or more head units (pc's) attached to tv's. I can't vouch for how easy or difficult it is to configure the myth as I haven't done it yet but there is a lot of support. The idea I'm working on is getting a mini-itx or nano-itx pc and use to boot a minimal linux os that can boot a terminal server session into either a linux running myth or a windows os running snapstream.

good luck!