Installing memory for dual core setup

Building new system. Have Athalon 64 bit dual core Processor (2.6 Ghz). 4 slots for memory. Have matched pair of OCZ 4GB (2X2) on order; one 1GB stick operating in single core mode now. Also have some other 1GB sticks in inventory. If I were to use the 1 GB sticks or any other combo am I right in thinking that the first 2 banks have to be matching, and when I get the OCZ-will the proc recognize the pair of 2GB and use dual core mode. Or is there a setting in the bios I need to change? Thanks for the help.....seems confusing to me.