Sorry, came late in on this one. I sell computer products, and build them. The first AM2 system we built was an ASUS board. Make sure that you strictly follow the manufacturers of RAM listed in the manual. The motherboard we used would only boot correctly using Micron 667MHz RAM, no other type of 667MHz DDR2 would work. The board states it was 667MHz compatible... but of course we all know this can be a lie. Also, all other RAM we tried worked (pertaining to your question, yes the lower speed RAM worked fine with all brands except OCZ). The weird thing about this motherboard was that it would not boot up with ANY speed or variation of OCZ RAM, so if your thinking high-performance RAM i would not suggest OCZ for socket AM2 yet, until they have aged a bit, or have some BIOS revisions that will fix the issues. All in all, the experience I had with the AM2 system was fine, except the finding of a compatible memory brand, other than that if we would have checked the manual first (RTFM), we would have been fine. Once the products have aged a bit, and we get some BIOS flashes ect.. I think the RAM issues will go away. The board we used was extremely fast, and all-in-all I liked it... The main reason I liked this board was that once we got compatible RAM installed, the system on startup just blows any older style boards out of the water. Within 2 seconds of pressing the power button, the system had already tested RAM, found all the drives, and had checked all of the drivers for bootable devices. Even after adding more SATA drives ect.. it still flew on startup. Anywayz sorry to go off topic with AM2, but that is my rant/ two cents.
Summary: Yes the boards will work with slower-speed DDR2 than 800MHz, but make sure u get a compatible brand (not OCZ), but if you can afford it, and have the patience, the system will work to it's full potential if you use 800MHz DDR2, of a compatible brand.
:twisted: