Use laptop keyboard as bluetooth keyboard

Hi !

Is there an application (on Windows,Linux, OSX) which would let me convert my laptop keyboard optionally into a bluetooth keyboard to control a pc connected to my TV like a media center.

Both laptop and PC have bluetooth. I would like to pair, switch laptop keyboard to BT, start a few things, switch back to laptop keyboard mode. Would be even better if I could do it from a Window Mobile PDA.

Right now I have a remote desktop/VNC setup.

-cb