I am wondering something...

Lets say that I get an ASUS a7n8x delx. mobo and it has 3 dimm slots. I buy a pair of kingston hyperX 512mb modules (total 1024mb) and they are working in dual-channel (in slot 1 and 2 or in slot 1 and 3). Then a year later I buy another 512 or 1024mb modules (it maybe the same kingston kyperX module or a completely different brand) for the last slot as an upgrade. Will i still have dual-channel? if so, how will it work?

Thanks