This product does not support Win9X/ME
Notice: Only DDR2-800 memory supporting JEDEC approved 1.8V operation with timings of 5-5-5 or 6-6-6 is supported on Intel Desktop Boards based on Intel 965 Express Chipsets.
Yet I see lots of builds and recommendations including from the manufactor's website with slower memory (DDR2-533 and DDR2-667), different timings and voltages.
It's just putting a restriction on the DDR2-800 memory that is supported. The JEDEC DDR2 standard states that DDR2 must run at 1.8v, and so the motherboard assumes it can give the RAM 1.8v and it'll be happy. But a lot of manufacturers intend their RAM to be run at higher voltages so it can achieve tighter timings. You'd have to manually increase the RAM voltage to whatever the RAM specifies to run its rated timings.
Basically, don't worry about it. If someone who knows what he's talking about recommends RAM for that board, it'll work- you might just have to go into the BIOS and increase the voltage and tighten the timings to get optimal performance.
No worries. When this and other boards first came out, it WAS a problem. Memory required more voltage, and no one could boot the first round of 965 boards unless they first used a stick of 1.8V memory to get into BIOS to increase the DDR2 memory voltage so that they could use sticks that used 1.9-2.1 (or more) volts.
I am using the DS3, though, and put in some Corsair 800Mhz 1.9V memory and it booted right up. Most everyone else has he same experience. I'm not sure what Gigabyte or other vendors have done to increase compatability, but I'll bet that the S3 will boot into BIOS long enough for you to increase voltage for whatever memory you are using