memory upgrade advice needed

I currently have 512MB of Corsair DDR XMS3200LLPT TwinX Platinum CAS2 (2 x 256mb sticks) on my abit nforce2-s motherboard. I'd like to upgrade the memory to 1GB and have one memory slot left on the board whats the best economic upgrade option available to me? looking for best web price and of course compatability with the current sticks... (i figure three sticks of memory should still be able to run in dual 400mhz mode like the current pair do?!?) also what slots would the three sticks need to be in for best performance?

as always, advice much appreciated

If you want one slot left (assuming you have 3 in total) then your best bet is to sell the current RAM and buy two sticks of 512MB PC3200 RAM. Crucial memory is excellent value.

Otherwise just buy another Corsair 512MB stick and put it in the third slot.

And yes, 3 sticks will run in dual-channel.

If you do just buy another stick of RAM of 512, then you should put the 2x256 in the slots next to each other, and the 512 in the slot by itself. That should letit run in dual channel.