vista parttion

I brought a new laptop acer aspire 4720. my hard disk capactiy is 160 gb. I created 4 parttion. 25gb,40 gb, 40 gb, 40 gb. all are primary parttion. i tried to keep 25gb c: drive as primary and rest of the drives as extended parttion. but i coudnt create extended parttion. so all the drives are in primary parttion. could any one please help me.
*********

i want to create exteded parttion keeping c as primary and rest of the drives as extended.