Dark Reign - Infested

For this task you need to go to the Broodlands. Once you zone into the Broodlands (north out of Lavastorm Mountains) follow the blue line on your compass to your quest objective. (If you don't currently have your compass up hold ALT down and press D (Alt + D)).

This is a very simple task to grind for faction. There are only five mobs you need to kill in total for it, four of them can be found in the rooms off of the main path (you'll know after you do it once what I mean) and the last mob can be found in the room right before the room that the raid boss normally sits in (in other instances and one in the static world).

I usually pull the entire zone, all of the mobs together and then AoE them down for the win. If you can't do this, running from one room to the other will work just as well.