I'm not sure of a good way to get rid of dust that is inside the projection system with most DLP models. Typically they have a sealed optical path which is designed to prevent dust from getting into the optics. I would call Optoma up and maybe raise some hell with them... At least I would start by asking them if they have a solution to this issue.
If the dust is on the internal optics, you should be able to bring it into sharp focus by adjusting your focus knob some.
