G41 chipset only officially supports 4GB DDR3 so it's one of those things you have to try. 8GB is only supported using DDR2 but your board has no slots for those.
All Intel Core 2 chipsets also only support 2gbit density DDR3 chips, which were the earliest type of chips made back in 2007. That means any 4GB stick must have 16 chips on it to work properly. And yes, the sticks must be desktop DIMMs.