Oxigeon

First of all sorry for my bad english. I have downloaded the free version of ArmaII because I first want to try the game of it will works on my machine. But when I do the first training mission the game is very laggy when i smooth with my mouse. When I push the up key the game do a little while before it runs. What can I do to make the performence better. I put al the settings on the lowest. My System: Acer X2 Dual Core Processor 5200+, MMX, 3DNow (2 CPUs), ~2.6GHz Memory: 2048MB RAM Hard drive: 630GB Video card: NVIDIA GeForce 7650 GS I play under Windows 7