What do you use the system for? What's your budget for the graphics card? What resolution does your monitor run at? What are your complete system specs?
AMD AthlonII Quad core x4 620 and 2gb or RAM thats it I havent bought a monitor yet will do tomorrow maybe you could advise i need operating system, graphic card, monitor ( i thought of getting a 19" hd lcd tv) and a keyboard and mouse i want to play games especially Arma 2 any help will be appreciated thanx!
What's your budget? You would be better off asking for component advice in the "Homebuilt Systems" section of the forum. There's a sticky titled "How to ask for new build advice" there. We can help optimize a build for you if you provide ALL the information in the sticky.
From the sounds of it your doing a lot of upgrading or a new build. With the limited info you have given another 2gb of ram would make a huge difference. For a 19inc monitor you don't need sli or crossfire.
As for operating system I would say windows 7 64 bit would make it more future proof its a lot faster than vista and runs better.
If your willing to spend a fair amount of cash for keyboard or mouse check out Razor products. I have a Lycosa keyboard and Lachesis mouse from them and all i can say is its like sex in yer hands. http://www.razerzone.com/
Sadly i cant advise on the gpu as don't know much about them.