There actually is no such thing as "dual channel ddr", as opposed to
"standard ddr". Some memory makers would like you to believe you need to
buy a dual channel memory kit for use in a dual channel system, but this is
not true; it does make them more money. Some people believe the best
performance is achieved by using the same amount of memory on each side, but
dual channel mode will work even if the sticks are different size or make.
See here: http://www.asus.com.tw/support/faq/qanda.aspx?KB_ID=84916
and here: http://www.nforcershq.com/forum/viewtopic.php?t=45999
and another discussion here: http://www.nforcershq.com/forum/viewtopic.php?t=45664
Check the manufacturer's web site of whichever board you plan on using for
more specific information. This question has been beat to death since the
introduction of the NForce2 chipset.