I thought we still had some Cat6 modules lying around..

If the TV is downstairs and the PS3 is in the loft, how are you going to control it from the living room?
And if it's for media, then why not play the movies through the PC which, if memory serves, is already in the loft?
If you have a windows based mobile, or can get your hands on an old PDA, then you can use GRemote over a wifi connection to control the PC with a cloned desktop display on the TV.
http://gbmsoftware.com/(Works on Android phones as well, and chances are they'll have something similar for the iPhone)