Thanks for the info.
Just so that theres some sort of reference my present system consists of : -
A Panasonic Viera TH42PX60, Pioneer Ax10i amp, Mission Elegante speakers, Pioneer Dv 989Avi and Sky HD (it took a lot of O/T to get all this!!)
I've already done some research and if I decide on a projector (Panny AX100 as stated) it would be with an electric screen (there are some on Ebay for around £180 that seem to get some good reviews on the forum) so that the plasma could be used for "normal" (I've got Kids and the projector lamp would need replacing every 2 months if it was the only option) viewing using a HDMI splitter.
That rules out the fixes screen option
The throw would be around 8 1/2' so a 6 ' screen would be the largest that would be I could have.
It would be in a room that's already warm (hence the fan!) and I am concerned about the heat the projector would throw out making it worse.
I hadn't considered aircon

it would be more expence (but then again I like my gadgets!!)
The light control would be taken care of with dark/heavy curtains.
I've worked out that the best value/performance option would cost around £1500, taking into account cables and HDMI splitters etc and it could be an expensive mistake if I screw up and the picture quality is not so good.
Would it be worth spending circa £400 for a "good quality" screen?
I could may push to £2000 if I wait a while
I really trying to convince my self that a projector is the way to go instead of another (bigger) Plasma.
There would be hell to pay if I screw up with yet another piece of kit needs another "upgrade"