Welcome to BleepingComputer!
I've played battlefield 2 and 2142 with only 1gb ram, even though they run better with 2gb.
Also, your problem could be your graphics card. Its not really that great, but you should be able to run battlefield 2 and 2142 on low settings. Here are some possible problems:
1. Your graphics driver is out of date. Go to nvidia.com
and download the latest graphics drivers for your card.
2. Your card might be overheating. Open your computer up and blow some air (canned air works best) throughout the entire case to get the dust and other crud out of it. Especially blow the air through the heatsink on your graphics card.
"I think there is a world market for maybe five computers." - Thomas Watson, Chairman of IBM, 1943