It also depends a bit on the motherboard. Do some research before buying and make sure your memory is on a recommended or compatibility list for the board. As I understand it, there is a very small list of validated DIMMS put out by AMD, which restricts dual channel memory at 200Mhz to single sided modules (which is not the case for most RAM.) However, the motherboard manufacturers (or most of them) have managed to work around this to allow double sided modules. Therefore, you're gonna get a longer compatibility list from the mobo manufacturer than you are from AMD.
Btw, don't get a Gigabyte 939 model as I did, they don't seem to have worked out the memory issues.