DIY Projector

If you don't mind dropping $15 or whatever it is, check out lumenlab.com. Besides a real nice how-to guide, you get access to all the forums where you can get answers to just about any question.

Like Madcraiz said, either spend the $20 for lumenlab (trust me, it is worth it) or go to diyprojectorcompany.com or diyaudio.com for free. Lumenlab is a must if you want the support for building it, and actually are going to go through with the entire building. I am in the process of buying my stuff, but I am also doing a whole home theater/media center make over. You will get people who know how to work very well with the physics of the projector, computer people, construction people, etc. All the people there have many different expertise, you will even learn a lot to merit spending $20 even if you don't decide to go through with the projector.

There are very few people interested in building projectors here at toms to merit an actual thread for projectors. You want veterans to help you out, so you will end up going to anyone of those other sites for assistance. I doubt there are really any DIY projector veterans here. The OHP design by the way is nothing compared to one built with a 1000W MH bulb, 17" LCD, 135mm lens, and a load of customizable addons built with an MDK casing for under $400-$500.