I'll put a plug in for MasterCopy
. It is a free, open source web app that makes projector alignment trivial. The idea is that you point the project at the canvas and then use your mouse to move the corners of your artwork into position. You can read more about it here
or go straight to the tool here
I wrote MasterCopy for some friends that were using projectors to transfer artwork onto large canvas flats for theater sets, but it works well for smaller, fine-art canvases.
Let me know how it works for you. I'm always looking for suggestions on ways to improve MasterCopy.