Fido,
The general quality of the DIY projectors is actually quite good - not as good as the latest and greatest of the newest projectors, but equivalent to something produced in the mid 90's (say, a Proxima 2800 as seen regularly on Ebay).
Most people start with a 640x480 LCD Overhead Projector panel built in the mid 90's and going for less than $100 from Ebay or various other suppliers (check out the old DIY projector thread for suppliers). When used with a high brightness OHP, the results are not quite full DVD quality, but are much better than a normal TV (if watched with the lights off).
Many people have replced the normal short-life halogen OHP bulb with a 400W MH general lighting bulb which gives out MUCH more light, and will last for 20,000 hours +.
In this configuration, much of the light is lost by the normal OHP optics, and while the bulb is not an optimal point source, the larger case and loose tolerances of the design tend to make this less of a problem than if you were to try and use one of these bulbs in a commercial projector. Some people have gone the next step, and created a new cabinet and reflector arrangement - but are still essentially using the OHP configuration in a single enclosed box.
I tend to prefer using as much hardware from a dead projector as I can because I am not very good with power-tools, and the commercial units are generally much more compact than something built from scratch.
If you are at all competent with electronics, and are attempting to cannibalise an old projector, I would first suggest completely removing the ballast and ignitor and storing them away - you do not want them accidentally hitting you with a 20,000V belt while you are probing around. Then, see if, using a lamp or torch as a temporary light source, you can get the rest of the projector to fire-up - look for leads going from the ballast to the main circuit board.
Commercial projectors, especially if they use three panels for RGB, are generally much brighter than those that use one panel (the type used by the OHP Panels). This is why some projectors give very high lumen outputs with only a 200 Watt bulb.
If you can get the basic projector electronics working, then you can figure out a suitable light source for it afterwards... I have done this with a number of projectors for myself and friends.
I sometimes re-use the old ballast with a MH bulb of equivalent electrical characteristics (different mount/reflector), or cobble together something using the more standard 400 Watt parts, but sacrifice brightness for quality - only using a fraction of the total light...
If you have an old dead light module, you might want to check out what type the raw bulb was - you might be able to find its electrical equivalent at the Osram web site - they have basic data sheets for all their bulbs, and you might be able to re-use the ballast, and/or parts of the light module.
Be careful, though, if you intend to play with these things - the bulbs are VERY high pressure, and can explode in your face if stressed.
Definitely check out other opinions than mine though - there are some awesome people working on this stuff!!!
Bill.
