In case you guys don't know about it, jbmod lets you "weld" any physics objects together and make anything you can imagine. For example here is an airpowered watermellon launcher I created.
http://www.personal.psu.edu/users/j/s/j ... al0003.jpg
http://www.personal.psu.edu/users/j/s/j ... al0004.jpg
http://www.personal.psu.edu/users/j/s/j ... al0005.jpg
It works the mellon goes about 1/4 of hte way across the map. Over at hl2world.com they had a watermellon throwing contest. Some people made full scale trebuchtes.
Anyways, heres a link to hte official board, it has links to all the essential files. There are also maps that have spawn points to create physics objects.
Honestly this mod rocks, A LOT.
http://www.hl2world.com/bbs/viewforum.php?f=43
Joe