Be careful before you buy your DDR400 memory for this board. It uses the VIA KT400 chipset which was originally intended to support DDR400 but in testing was found not to work well with some DDR400 memory (also in those days, there was no official JEDEC standard for DDR400 yet). VIA was forced to give official support only for DDR333.
It can still work with some DDR400, but no guarantee. That is why most mobo makers have a list of DDR400 models which have been tested to work well with the mobo in question. click here to see the list for this mobo (and note the limitation for using only up to 2 banks of DDR400 memory). The list is probably old, and things with DDR400 may have moved on a bit (with an official standard for DDR400), but don't take anything for granted.
The other possible limitation with the KT400 chipset (but I can't find it mentioned on Asus), which I have seen on another motherboard using the same chipset, is if you use a Barton CPU with 333 FSB, it cannot use DDR400, or rather it will work, but the memory can only run at 333MHz. No such limitation if the CPU has a FSB of 266 or 200 MHz on that other motherboard. I can't remember the make of that other motherboard, but the information came from the mobo website which says this limitation is one caused by the chipset KT400. Whether this applies to Asus I don't know.