What version board are you running. There are 1.3, 1.4, & 2.0. It will be over where the Floppy drive would plug in.
If you are running 1.3 there are two bios updates for: Improve memory compatibility
If you are running 1.4 there is no bios update:
If you are running 2.0 there is a bios update for: Adjust DDR over voltage function.
Plus this what they are saying on the spec's on line.
DDR3:
2 x 1.5V DDR3 DIMM sockets supporting up to 8 GB of system memory
Support for DDR3 1333(O.C.)/1066/800 MHz memory modules
DDR2:
2 x 1.8V DDR2 DIMM sockets supporting up to 8 GB of system memory
* Due to Windows 32-bit operating system limitation, when more than 4 GB of physical memory is installed, the actual memory size displayed will be less than 4 GB.
Support for DDR2 1066(O.C.)/800/667 MHz memory modules
Dual channel memory architecture
(Note: Mixed mode, populating DDR2 and DDR3 memory modules simultaneously is not supported. Please refer "Memory Support List" for the latest supported memory speeds and memory modules.)