Will they be compatible to run on a motherboard supporting 2gb of memory? Will there be any effect on the system performance or any other components?
A DIMM, or dual in-line memory module, can be any of the following:
for more information please post make and model of the mainboard and memory you want to use.
edit: the specs are pretty clear on the typ of memory the can be used with your mainboard:
that means you can either use 2x 667 MHz or 2x 800 MHZ DDR2 memory, and no you can't mix them.