According to The Inquirer it's possible that AMD's Socket AM2 platform may support 400/533/667/800 and even 1066MHz DDR2 memory:
By integrating a memory controller onto the CPU die, the company has full control over information and all that motherboard manufacturers have to do is make a voltage regulator for the DIMM slots and some trace correction on the PCB, if necessary.
What surprised us was a talk with one of rhw motherboard engineers. Our source claims that AMD's Socket AM2 delay is actually the by-product of "engineering change at (the) last moment". He claims his company has to redesign the PCB more than "others", since they need to support DDR-II 800 and DDR-II 1066 memory standards.