Thanks ivor, thats the kind of inspiration i was looking for tbh.
I've just come back from ikea having had a look at what i could buy or buy/modify of theirs to suit, but in all fairness if i build it myself it can be done 'exactly' how i want it.
I rang my step-son earlier to ask him to get to work designing me one using sketchup which he seems particularly adpet at. He's only 15, so is hopefully quite enthusiastic about getting it done.
After all even though the 42" is going in the new extension it means the 32" Toshy stays with him and his brother in the living room, for their xbox360/wii gaming pleasure.
I've knacked me back in (again) so all i can do tonight is start planning it all out. Thanks for your help, will post again when i have further questions.
ps....chasing out the walls isn't an option now, since i've spent months building the damned room, i'm not about to start knocking holes in it again and making more mess.