A square picture?
There are no projectors that are intended to deliver a square picture. Your standard format 4:3 frame is as close as you're going to get. And these days, the trend is toward widescreen formats, with 16:9 being a standard. It's the standard used by high definition TV manufacturers.
My personal bias is toward CRT projectors. They ARE big, heavy, and require a little bit more
in the way of setup than a digital projector, and need some minor adjustments from time to time
to continue to deliver their best picture, but they have flexibility and versatility that no digital
projector can match, they can easily outlast ANY digital projector if the CRTs are relatively new,
and the picture quality of the best CRT projectors is simply better than any digital projector you
can buy, period. (A very biased opinion of mine, but based on what I SEE.)
CRT projectors aren't for everyone. You should be the type who likes to fiddle with a bunch
of knobs and settings, at least every once in a while, in order to be well suited for CRT projector ownership.
It's tough for me to recommend digital projectors because all the ones I've seen that delivered
what I'd term as an acceptable picture were all quite expensive.
I'd recommend you visit your local audio/video specialty stores and see what they've got. Get some ideas.
Visit www.avsforum.com to get some good information, too.