This has been done before, IIRC Samsung released one of the first TV quality raster scanning system for laser shows.
Basically a standard laser show setup uses multiple lasers (to get your RGB) combined into a single beam then passed through a device, such as a PCAOM, which acts as rather like a programmable colour filter. (this isn't the only way it can be done with solid state lasers).
Two sets of mirrors can be steered in the X and Y axis to draw your shapes, beam effects, etc.
In the case of a TV or other raster displays the beam is steered much like you would an electron beam on a regular TV. It scans a horizontal line, moves down scans across, repeat. You can switch the direction of the scan (left to right, then right to left) on alternating lines to speed up the scan rate.
Wikipedia has some info on Laser TV's in general: http://en.wikipedia.org/wiki/Laser_TV and LaserFX has some info on PCAOM's if you're interested in the older tech: http://www.laserfx.com/Backstage.LaserFX.com/Archives/Archives6.html
Early systems actually used multiple projectors overlapping or drawing the first 3rd, 2nd third, etc of the image to make up for slower scan rates.
I took a fish head to the movies and I didn't have to pay. -- Fish Heads, Saturday Night Live, 1977.