You can never have enough ram, recently built a machine for my missus with 2 x 2Gb of Corsair PC3200 (yes, it did cost me an arm and a leg!!), she used it for 3D rendering and it flew. I played some games on it and it was tremendous. Sold the system in the end, as someone offered me a profit of £500 on it!!!
I truly recommend any new system build to have at least 1Gb of ram. This is also one of the reasons you see so many people on forums selling their 256Mb sticks as they are looking to upgrade to more ram....