It might be possible using "Theatre Mode" in Catalyst however I'm not sure if the remote will be responsive because xmbc may not be the active window. So two ifffies there: Is your vid card AMD or does it support a "Theatre Mode". And: How does your remote interact with your PC?
Or if you found the older jailbroken Apple TV 2, you can load XBMC on it. I have 2 with XBMC, and at [email protected] they are a cost effective solution. Small, use very little power, and 720p. Plus they have Netflix and the ability to rent movies. Wireless, works with any remote amd HDMI. Newly released Apple TV2 will be hackable soon.
I think the reason you're not having a lot of luck searching for a solution to this question is that it's in large part it is hardware defendant. Using my HD ATI graphic card... I can have XBMC operational full screen on the TV while computing with win7. But many people find issues with an extended screen set-up and full screen taking focus, leaving them unable to do O/S tasks. Sadly they end up using 'Windowed XBMC' - cpu/gpu intensive mode with normal window gadgets showing up on their TV.
Set-up your normal extended desktop across the two devices... run XBMC in windowed mode... drag the window to the TV (or second video display) and use the \'slash key' to enter full screen mode...
PatK has it right. It can be done but their will most likely be no remote control of XBMC. There may be solutions that will provide separate "hooks" for the remote but I don't think XBMC will do it as provided. The other problem with XBMC is that it usually wants to minimize when it loses focus. It may be possible to run the XBMC session in a virtual machine but that requires some decent RAM and CPU power, not to mention good video emulation, and the remote control input issue still needs to be resolved. Obtaining a cheap media player or a second PC for HTPC use may be the best solution.
This is one of the reason why am using Serviio instead. If you got a ps3, Xbox 360, or any dlna capable device connected to your TV it the best way to go. For that matter most recent middle range HDTV have media center connectivity already!
You get a lot of the XBMC functionality without having to physically connect your PC to a TV that likely already networked one way or another anyway. I was a long time user of Mediatomb but since that project is pretty much dead I would not recommend it.