I built a frame 8 feet wide and about 4 foot 'tall' it is fine with my projector at about 12 foot distance (I am using a 17" LCD and Pro lenses). The screen came out great. I stretched BO cloth on it.
But the problem is the picture is great only on widescreen which I thought would was gonna be the only format I was gonna use... however last night my daughter asked to used her computer on it with her games like WOW and Guild Wars, etc... but the picture is almost 9" tall! The only thing I can think of doing is to either build a new screen or add an extension to this one.
I was thinking of building a section the same width (but not as tall of course!) I would butt this up against the other screen and attach it with metal straps.
Has anyone tried this? I am considering (quite strongly in fact) that I will be painting the screen with a Tiddler paint recipe so that too should help 'blend' the line better.
What does everyone think?

Couldn't you just change the resolution on the other computer so that it fits on your existing screen?

PowerStrip 3.7
http://www.entechtaiwan.com/util/ps.shtm

Thanks for the reply.
I thought about doing that but my daughter wanted to play it BIG, not a dinky little 4" X 8" screen!

Hey my daughter says the same thing.. When we watch a movie I have to crop it or reduce it to fit on my screen which is about 8x5 .. of course at full screen my old projector would go about 11x8 I just didnt want to have the whole wall as my screen.. Our bedroom wall at the apt is only 8x14 but if you open the bathroom door it covers up about 2 feet of the wall .. What is funny is we have a 56 inch wide screen 1080i rptv..in our den hooked up to HDMI and Optical audio thru a killer surround system but my daughter perfers to watch the projector and she says that now all the screens look small... Maybe I should just buy a movie theater

It is hard to deny the appeal of the big screen experience. Especially playing games. It is so much more immersing when the image fills more of your field of view.

As far as using the whole wall, why not. Just give it a good sanding and apply a good quality paint like Behr Exterior Premium Plus Ultra. Leave it white or use a neutral gray tint. When the pj is off it is just a gray accent wall. When the pj is on it is a nice big screen. You may even consider projecting some nice soothing images on the wall as artwork when it is not in use.

With respect to the OP, adding a section of BOC. Unfortunately you will probably see it in the image. There is a seller on eBay that sells very wide BOC. You could make a 4:3 screen.

Right now I am renting the house I am in and the only wall that is big enough to turn into a screen as a big window in the middle of it! (the lady that owns the house would probably get mad if I filled it in!)
Maybe I will make a whole new screen and using the larger BOC you mentioned... and save the teenie-weenie 8-footer for a small room!