i got the one with 1gb of ram and 2.8ghz processor thats 24' screen. i want to install more ram when it comes. im going to order some ram and i want to know if i can buy a 1GB ram stick and stick it in my iMac. i read that it comes with 2 512mb sticks, so can i have a 1Gb stick and the 2 512mb stick i n and it will be 2gbs? and how do i open it?