Hi jcshutts
Just my pennith a long time ago, well afew years ago I played with this idea, the lounge was being decorated anyway so allowed me to try this out, I bought some quality emulsion I used matt, then went over with it with silk, funnily enough matt gave the best result, dont ask why I have no idea..maybe reflection,like BB said I did mask the edges with black tape, I allowed 2in around the edge this allows you to set/fix the image. The projector I had then was a runco just 720 componant then, great projector, the results were very good indeed, however the down side is I could not keep a wall white all the time exposed, so this would mean a space that had to be kept clear, well almost but remember if you wanted to use it I had to clear everything, but I was only trying this out. So you would need to keep that in mind, however although the results were very good,like yourself a decent screen, motorised, tab tensioned or what ever was out of my reach, although there were some reasonable bargains second hand, in the end I bougt a brand new manual roll down screen, I paid £160 delivered as I recall and the results were brilliant, they were better than a painted wall easily. So the things to think about are, how much will a good quality paint be, do you have the space to keep pretty clear when you want to use it. Screens have come along way now so getting a good screen will not be out of reach, plus when you have finished you can just roll it up out of the way, so any pictures and the like on the wall will be seen again, the fitting of manual screens are easy peezy either ceiling or wall,usally with 2-screws thats it, and remember with a screen be it manual motorised you are not limited to where it can go, within reason but a painted wall would need to be pretty much free of anything and be the size you would really like.
I have gone on abit here but this is not just a case of brush paint, :look honey I have decorated the lounge: what do you think??? have a look around the web flee-bay other forums and I am pretty sure you will be Ok. 8)
Also the gain of a screen is important, so what ever projector you have or will be getting make this is not overlooked, the gain is the shade of the screen and determins the brightness of the image, plus some other things but its been a long time so do a little research. :O