Looking at you system - it's quite well balanced. This is good news - and bad, as upgrading one part probably won't have a dramatic effect on it's performance. If you want to play fairly current games with acceptable frame rates you really need to upgrade your cpu, memory and graphics card.
If you check out the minimum specs required to play MOH (for instance)your current pc actually exceeds them. However I suspect you will find the experience unsatisfactory and frustrating.
Sorry it's not better news - perhaps some else will have a different view?