I'm pretty sure that because it's a 2gb and 4gb stick, you're only running single channel. You would need either 2x2gb or 2x4gb for dual channel. As for the speed, they're most likely running at 667. Both sticks. They cannot run at separate speeds, and the listed speed is not always the default speed. I'm not certain about DDR2 RAM but with DDR3, the highest JEDEC spec is 1333mhz so if you buy 1600mhz, 1800mhz and higher RAM, it's going to run at 1333mhz by default and you need to manually overclock the speeds to reach their rated value. I'm sure your 800mhz RAM is the same, but 667 might be a default speed.
Either way you can easily go into the BIOS and see for yourself, or even just use CPUZ in Windows.