i have installed a new trigger group on my ak. i know they are not the same but, are the ar triggers much harder to install? do i need any special tools? i am thinking about the rock river arms trigger. what do you think of those?

look here.

All you need is a punch, piece of cake to install.  I can highly recommend the NM Rock River trigger as tuned by White Oak Armament.  I have 5 and they are fantastic.  I decided to cheap out and bought two RR NM triggers from Brownells, for a NM trigger they were lousy, they had 6 pound pulls.  I sent those two to WOA for the 3.5 pound trigger job and they came back perfect, so I ordered two more already tuned triggers from them.  Those were perfect also.  The only problem I have had is on my .458 SOCOM upper when I used the JP Enterprises rear tensioning pin, it bound up the bolt carrier.  The BC was dragging on the top of the hammer.  I called RR and they set me straight, stone off .001" at a time until it no longer drags.  After I removed .003 inch from the top of the hammer, perfect, and has run perfect every since.