No it doesn't,it only supports DDR2 RAMs
Anyway,in games you won't see a noticeable difference between 4GB and 6GB but in heavy image/video editing you'll notice a small boost in performance
You would have to upgrade everything to jump onto DDR3 platform. and by everything i mean Motherboard, CPU, Memory. (3 of those will boost your performance)
There won't be any noticeable difference if you only upgrade memory (**)