Difference Between 32 Bit (x86) and 64 Bit (x64)
You will only get 3.2GB recognized. Be it dual channel or single channel. Which ever you are running. So if you are running Dual Channel it will be dual channel. That doesnt affect it at all.
The RAM speeds are independent. You wouldnt double the speed cause it is dual channel. They will still only run at 800 MHz even in Dual Channel mode. Since your mobo is only configured for 400MHz they will only run at that speed if the RAM is capable fo running at slower speeds.
No. Ram stick and RAM Module are the same thing.