Hi Dusan, check you processor support of your capacity of the RAM, not all motherboards supports all the DDR2 modules like you mention. I think 2GB is enough for this computer. It must be the same bandwidth to speed-up your computer, ex. Two Modules each have a 1gb of DDR 2 800Mhz. Installing different bandwidth can slow-down the speed of computer, because computer system needs synchronization through the processor speed and bandwidth including the capacity.