Transparancy

Im sure this subject has been covered quite alot in recent times. I understand the blending technique, and have used transparancies before. The problem i''m having is partially due to the fact that transparent objects have to be drawn twice, obviously a great consumer of processor power. Ive heard alot about alpha values, and not drawing colors which correspond to a certain alpha value. Ive looked at the TGA loading tutorial, but am not quite ready to go through and understand all that right now. But now to my question: Does anyone know of a simple way to ignore a certain color when loading a bitmap (for transparancy)? Cheers again ppl -- Wav