Ram is not dual channel, the motherboards are.
You basically need two sticks of ram, put them in the appropiate slot, and if your motherboard supports it, it will be in dual channel. The 2 sticks work together and gives you double the bandwidth e.g. for PC3200 it would be 6.4gb/s bandwidth over 3.2gb's worth of bandwidth in single channel. If put on a AMD board, it gives a nice boost in performance due to the memory controller on the CPU. Intels don't get as much, but it is still a nice boost for the price of getting 2 sticks over one, which can be cheaper.
It won't give you twice as much performance, less than 50, less than 25% if you find a bench test somewhere it will tell you the exact increase.
Cisco CCNA, Comptia A+, 1/3 through CCNP