With out knowing more about the table structures/evironment, I can't get specific, but I have been playing with some query optimnisation tools, and the order of things in the WHERE clause can have an effect. It may be a big thing in only 2 tables, but, try ordering you where so that the clause that eliminates the most records is first, then the second etc.
I'm not sure if that helps you any, but It will save some query time.