the RAM must be the exact same model and specs in order to work. You have one set of DDR and the other is DDR 2 according to your post, not to mention they're different size and maybe different Mhz. Remove the 1gig RAM and use the 2Gb in their respective slots in order to use dual channel. Remember, they need to be the same spec and model, and installed in the right slots too. Consult your motherboard manual for details.