Seems like there are at least four ways for a teacher to have a classroom see and interact with a single computer screen:
1) Promethean/Smartboard solution where you buy a screen and a projector at around $3000 installed, I've read a lot of the value is in the software -- it's easiest to make the highest quality lesson plans using their software (and they have the largest selection of lesson plans to borrow from other teachers)
2) Mimeo/eBoard solution where you buy a doodad and a projector for around $1500 installed. The software for this is apparently not that great.
3) An interactive projector solution where you only buy a fancy projector for around $1500 installed. Again the software is supposed to be not that great.
4) And there is a different solution where you don't have the big interactive screen at the front, but instead you do the interaction remotely from a tablet the teacher holds. So you buy either by a PC tablet and a projector or you get iPad/Android tablet and a projector:
I started a conversation on ISED to see what others thought. My initial opinion is an interactive projector is the best short term solution for my school; if we are 1:1 eventually then I lean toward iPad+FlatscreenTV which seams like the sexiest solution. But I have no idea, I've never even seen most of the stuff I read about.