Photo of Windows 7 Media Center with Touch Interface (from Gizmodo)
The guys at Gizmodo were in Redmond this week and have a quick video showcasing Windows Media Center 7 controlled by touch. That would be touch control integrated into the OS so no 3rd party software needed. It looks smooth and could be useful for those wanting a touch-interface for their HTPC.
See the video at Gizmodo
If you are wanting touchscreen now, HP Touchsmart has it and SageTV has a nice TouchScreen interface that you can use now if you have a touchscreen monitor ;)