passlock on GM vehicles

ok i have never worked with a GM vehicle equipped with the passlock system.   my neighbor wants me to install an alarm in his 99 suburban.  to my understanding...all GM vehicles 98 and up have passlock so i guess his does.  he had a factory alarm, but lost the remote so he just wants me to install a new one...he said he didnt like the factory anyway.  so what is the deal with it....what do i have to do if i have to do anything to bypass passlock?  can i not hook up a keyless entry function on an aftermarket alarm with passlock on a vehicle?   since he had keyless factory, all i have to do is trigger is factory relays anyway.  im confused being that i have never dealt with passlock before so if someone could explain how it works and all i would really apprecitate it!!

You can put the aftermarket alarm/keyless on his suburban no problem, you're right, all you have to do is trigger the factory relays (must use relays, set up for positive trigger) located above gas pedal....The only thing you would need to worry about passlock with is, remote start, then you would need a transmod to bypass the passlock system on his truck.