Rdram is a kind of computer memory, the differences from other memories (like ddr ram) are technical and don't have relevence to half-life 2. 512MBs is enough for Half-life 2 to run. Valve will be releasing a benchmarking tool for users to see how well their computers will run half-life 2, when it's released, get it, then you can see if the other parts in your computer are adequate based on its results.
