that's all you ask for, go into store and ask for DDR2-667 Mhz memory, I would say ask for Kingston, Crucial or Corsair brand of memory. Kingston has the less amount of issue and with a limited lifetime warranty you will not have to worry about that for awhile. You should buy it in a kit for best performance but that all depends on how much you have currently and how much you need. Now don't worry id f it say PC-3200, or what ever, when you ask for the DDR2-667 you are being specific enough to what you need that you don't have to know the other number, heck I have DDR3-1333 memry which is like PC3-10600... well close to that number, I am a Network Administrator and I don't even pay attention to that, just get the speed I need. Hope that helps
The above link gives the compatible (tested ) memory modules for your mobo..
The model naming is done on the basis of peak transfer rates.. For a PC2-6400 memory module, PC2 refers to DDR2 and 6400 refers to the peak transfer rate in MB/s of memory at 667 MHz.. Thus a PC2-6400 memory module means a DDR2 667 MHz memory module..