Can I use Commercial Projector parts? Probably not. Most commercial projectors, like the camera lenses, are made for small screens. While there are some projectors which may be retrofittable, these will tend to be the larger units. The lighting gear is generally inappropriate as well, and expensive to boot (this is one of the advantages of DIY, after all) so you may not want to use that.

In summary:

Lens: Nope. Not unless you have an LCD that is the size of the one in your commercial lamp or smaller. Don't count on it being good for anything larger.

LCD: Well, maybe. But then you're better off retrofitting or fixing your commercial projector.

DLP: No. Definitely not. A DLP requires a known light source size, so even retrofitting a DLP is an iffy proposition. Fix it or chuck it.

Ballast: Sure, provided that you get a compatable lamp.

Lamp: Isn't the high cost of lamps why you wanted a DIY in the first place? (Aside from the cool factor, that is.)