That'll be a clear case of RTFM, because that's entirely dependant on the mainboard layout. Typically, you'll have to put your DIMM pairs into adjacent slots. Also, on DDR2, you need to populate the slots farthest from the RAM controller chips first.
If the DIMM slots are named A1, A2, B1, B2, I'd say you go for A1 and B1 first ... but that's just an educated guess. Read The Fupplied Manual