I decided to submit this instructable after the trebuchet was already built, mostly because I wasn't sure how it would turn out. But I took some pictures and have a few videos so you can get an idea of how it works and how it was put together.
One additional comment before we get started. I'm really not sure what the range of the trebuchet is, considering I cannot test it outdoors because of the weather. However, adjusting the range is pretty easy though: shorter sling yields earlier release; shorter boom tip yields earlier release.
Also, there are plenty of cool ways to rig up a trebuchet, this is just the way my roommate and I did it. Have fun and be sure to shoot as many projectiles indoors as you can (I recommend practice golf balls).