Mobo/ram question

I have this motherboard:

When it says dual channel support: yes, does that mean it can use ddr2 memory?

Also, right now I have 2 x 512 corsair xms. Could I possibly put in a 1gig stick and have it work fine or should I stick with 512 sticks.

I know I’m supposed to match the speed of all my ram. So if I had some ddr 400 that means I can only get other ddr 400 ram right?

Thanks

SR