Originally Posted by Parrelium
So do I just go [antenna-power injector-3 way-splitter-Hauppauge WinTVhvr2250+TV]?
Then can I broadcast from pc to each xbox in the house using WMC?
More or less. There is really no reason to connect the antenna directly to your TV outside of having one more tuner (the TV's) which of course you can only watch live... I watch live perhaps 2% of the time. Commercial delayed more than any other... start viewing after the recorded buffer exceeds the total time of commercials.
One last plug for external tuners. Especially, if you plan on having multiple displays including other PCs. You can use the tuners independently of the main (server WMC HTPC). This way if for any reason the main PC is offline you can still watch TV at any of the other PC locations and even record. I know many are happy with built-in tuners just conceptually I'll avoid them if possible. Two or even three tuners aren't going to be near enough anyway if you begin to really use various sets around the house.
Regarding the second part yep... all you do is register each Xbox with WMC and you are good to go. Pretty much whatever you can do via the main HTPC you can using the Xbox. Within the TV scope of WMC. I don't rely on wireless (again avoiding it if possible) but I had success in using it throughout the house with the Xbox.
Best bet is to install WMC and give it a go... quickly you'll discover a few issues unique to you and several not so much. Overall it simply works.