Hey the Big man ! Usually there are minimal requirements and then recommended requirements for playing any game. With only 1GB worth of RAM, I'm guessing you're using Windows XP, since Vista won't run properly only on 1GB worth of RAM and 7 will struggle X_X (or it's a mac.)
Best way to find out what RAM you may need is take out the current RAM stick and post the information on the sticker here. I'm guessing it may be DDR or DDR2. Also how many memory slots you have on your motherboard may help us make a good choice :) !