it's never a good idea to mix brands of memory.

I'm going to go in a slightly different direction. I have DDR which supports dual channel. My FSB = 800mhz But my RAM runs at 400. Is it possible to go from a 200 pin pc3200 SoDimm that runs at 400mhz to something like a 200 pin Pc5300 SODimm that runs at 667 Mhz?

no. Your motherboard will only support the max type specified. If you mix ram, it will run at the slowest speed available if it doesn't work or burn out your system first.

read the ram guide in the guides forum.

I have a weird problem when I try to run dual channel RAM, when I boot the computer up it runs for about 4 seconds then shuts itself down for a few seconds, then boots itself up again, and the process goes on until I cut the power. I know dual channel mode works because the computer has actually worked with dual channel a few lucky times. Anybody have any ideas on what is wrong?

Some BIOS come with the option of setting dual channel on or off, turn it on only if you have two matching sticks. Remember as far as matching RAM goes, size doesn't matter, you can have dual channel RAM with a 512 and 256 sticks and still be dual channel if they are matched.
(Hendo, please start your own thread and do not hijack other peoples threads.)
cheers
Hynesy