'lo :) Nice idea - there's been some discussions this year - especially in the CRT projectors forum, about both "stacking" two projectors to get one brighter image the same size, as well as two side-by-side projectors to generate a wider image - Typically with the projectors the "Normal" was around, not on their sides.
There are tricks for certain high-end CRT projectors to help get the edges of each picture to blend together seamlessly, and with the same colour balance/white point etc etc... These could be harder to recreate on "Mainstream" digital projectors where "White" depends on lamp life etc.... However a digital projector wouldn't suffer from convergence drift which is the main headache in the CRT solution.
I've just returned from Photokina in Cologne - a high end camera & display show - where JVC were demonstrating 3 of their ILA projectors (model 4000s I think) producing a perfectly crisp and bright ultra-wide image... Each projector had a special attachment over the lens which must have been assisting the blending - but the result was an excellent image free of "joints"
....They also had their QX1 top-end projector shining onto a 6m wide screen, proving without a doubt that money CAN buy a *perfect* image if you have enough of it - and from only one projector....