Motherboard with DDR tri-channel - Do you have to run it in tripple mode?

[NeilF]

If you buy a motherboard that supports tri-channel DDR, can you put regular (cheaper) dual-channel DDR3 in?

 

[NeilF]

Well, looking at OC for example, they only sell one set of it, 12GB=£120!!!

Or I could just get 2x4GB (dual 8GB) (enough for the PC) for £50 - http://www.overclockers.co.uk/showproduct.php?prodid=MY-118-GL&groupid=701&catid=8&subcat=1516