Heres what I've done so far... it used to work.. It's got an error now I beleive they just updated the packet structure of the action type packet since i last played (june 06) so its an easy fix. Have fun.
You need java of course :P, and teh rest is pretty well known.. Original source i modified is included along with mine. Aimbot works and all.
*Edit - Link removed, April fools joke, by a1blaster*