asterisk users - Sep 2003 - Group pickup codes, etc.

Hi people,

I've got Asterisk running nicely with two 7960s and hooked into our 
MD110 via a cisco AS5300.
All is wonderful with the world...except, what is the deal with features 
like group pickup and so on...
I have no idea what codes are available, what they do, etc...is there 
either a standard * is conforming
to, or some doco of what features are available? (heh, yeah 
right...doco...what AM I thinking?)

Thanks,
Daniel.