Hey i have a 20" iMac 2.66 /w 2 gb of ram. And i use my mac for everything! but im having trouble with the ram. Like the more programs i use the more ram it takes.. but when i close it, it only releases a few memory space and i end up having 100 mb of free memory at the end of the day. Is upgrading to 4 gb necessary ? Also is it necessary for gaming? Like COD4.