Check out my website, http://www.siegethedayinc.com . I make and design catapults for living. While I have a copywright on all of my designs and they are my intellectual property, I don't mind if you reverse-engineer them for your own use...in other words, not for profit.
That said, I have designed mousetrap and rat trap catapults, and there are pictures of them on the website.
Also, feel free to contact me through the website for advice or questions.
In regards to having to add anything to a mousetrap to increase its power for launching acorns: Don't bother! My design will easily launch an acorn 35+ feet with authority...lol!
Scotsquatch