Upgrading RAM

My System Profiler says that both my RAM slots have DDR SDRAM PC3200U-30330 in it, which I would assume is PC3200 (330) however the Apple Support page regarding this says that the iMac G5 (Ambient Light Sensor) contains PC3200 (400). I want to buy 2x1gb to replace my current 512mb & 256mb sticks and I want to make sure I'm buying the right ones.

The easiest thing to do would be to take a look at the Memory Advisor on Crucial.com. That will tell you exactly what kind of memory modules you need.

Thanks! Didn't know that place existed. Much appreciated.