I would use 1 gb sticks in the 2 empty slots. Use the cpuz readings to match the memory chipset maker and timings. At crucial.com, crucial has the "memory configurator" software to match your dell memory. It's guaranteed to work. Newegg may be cheaper, but charge a 15% restocking fee if it's memory doesn't work. They had some ocz 3x1gb of ddr3 for $27.99 after rebate, but I don't know if it will work with your dell. If you can't get a decent price on 2 sticks of ddr3, I would just leave your system alone and let prices come down more. You won't notice that much difference between 4 and 6 gb of memory, dual channel or triple channel.