The Simpsons have never had a Star Wars episode as far as I know. Family Guy has had two, I am not sure if a third is being made though.
I think a Simpsons episode would be pretty good, do you? Or would it be more of a copy of Family Guy. I like this poster someone has drawn, interesting that there is no Darth Vader (I know Vader wouldn’t be in this scene but just about all posters have Darth Vader in it, don't they?)
I thought I would just look up about Star Wars Family Guy and there will be a third episode – called Family Guy It’s A Trap, out in December. Looks like Carrie has a voice role in this one. Here is a picture of the DVD cover.