I'm pretty new to wheel building, but I'd like to get into it. One step closer to frame building.

I do a lot of singlespeed mountain biking and I commute on a fixed gear. I'd like to build up a new rear wheel for my singlespeed and some day I'll need to replace the rear wheel on my track bike. I've heard talk about singlespeed or fixed gear wheels not needing to be dished. Is this true? If so, why?

Is there a good wheel building tutorial or guide specifically for singlespeed or fixed gear wheels?