ASE Labs posted a review on the Kingston 2GB PC2-9600 KHX9600D2K2 memory

The modules are regular DDR2. They are tested up to 1200MHz (Yes, 1200MHz!) at 2.3 or 2.35v. This is where the PC2-9600 comes into play. At a speed of 1200MHz, most people will not be able to use these modules at all at the rated speed. This is why Kingston made sure these modules also handle lower speeds and tighter timings well as well. Since my system could handle the 1200MHz memory bus, I cranked it to that specification.

Kingston 2GB PC2-9600 KHX9600D2K2 Review