Collective info on Serbian administration (Belgrade)

a friend of mine is about to come to Belgrade and settle down here / his gf is in Belgrade, and he also wants to look for a job. I will be away for quite a while, unfortunately, and can't help him with bureaucracy issues - is there any website where he could get all the info on how to apply for a work permit and where he and his gf should register him? is it any police station? they are engaged, can he get a permit stay? etc.
I tried the eng.version of MUP page, but it didnt work.

any recommendation is welcome!

Thanx, Marina