sli motherboard

i have an spare celeron d 2a processor and nvidia 8600 gt graphic card .(pci express)
i want to buy a motherboard that will support sli configuration for the 8600 gt graphic card. i will buy one more card ie 8600gt to use in sli.
i want a mobo on which i can use my celeron processor the 2 video cards . i tried to google but i was getting mobos which supported sli but in 8x . these mobos when only one card was used they supported 16x but when used in sli it got split in 8x.
can any one suggest which will support 16x for both the pci xpress slots.