Eyefinity is a term used to describe using a single graphics card to display two to six monitors. If you look at the AMD (ATI) Radeon HD5xxx and HD6xxx series graphic cards, you see those that are Eyefinity capable. As far as what software you need, just the drivers for the graphics card.
Yes, I suppose you could set up a curved projection screen and watch movies. Personally, I find one projector to be sufficient, but if you really wanted to, yes, you could go with three projectors (and three screens).