1GB of ram should be fine. It might be a bad card. Can you remove one of the previous cards, and go back down to 2 cards while testing the new one?
Hey there Crazyates, hows it going? Not seen you around much recently.
Oh.. all cards are fine. I've mined with them all. It might be a mobo problem?
Oh hai thar! Ya I was out of town for the past week, and just got back.
What MB do you have? Try disabling all the stuff you don't use: wifi, firewire, audio, secondary SATA, etc are the common ones to start with. If you're not using it for mining, turn it off.