vista 64 bit with sli 280 nvidia cards

I have just installed windows vista 64 bit with 2 nvidia bfg 280 1gb
cards - I now find myself in the postion of not being able to enable
sli from within the nvidia control panel - the option just does not
exist - i have a asus striker 2 extreme motherboard with the latest bios
- i have the correct chipset drivers etc, the correct nvidia driver, any
ideas anyone?

I would assume this is driver related, but nvidia say their driver is
64bit compiatible which is trust as they are usually very good, could it
be the fact that i have 4 gb memory and the extra 2gb video memory from
the graphics carrs which is somehow stopping me seeing the sli setting?

has anyone else had this problem?