Best advice I could give would be to check out the documentation for your mobo. Under the section on memory, it'll tell you what slots to place your sticks and if you'll still have dual-channel or not. For example, let's say you have slot A1, B1, A2, B2. For dual-channel to work, you need identical sticks in A1 and B1, going on that logic you may be able to put that 512 stick into A2, and maintain dual-channel operation on A1 and B1. Give it a shot, if it works great! Otherwise, no harm done.