I'm not sure if it would be duel channel or not, but after you turn on your computer and it posts, it will say on the screen "duel channel activated" if it is. But I don't think you can run duel channel with all 3 mem slots being used. But you will know for sure by looking at the screen during startup.
As far as installing mem, you should use DIMM 3 first, then DIMM 2, and then DIMM 1, in that order.