Bear in mind that just because it's from the same manufacturer and has the same part number does not mean it will be identical. Sometimes you will get different chips on the PCB, manufacturers do switch around, especially with value RAM - they just get whatever was cheap at the time, since because RAM is a commodity the price fluctuates like gas (except the price tends to go down over time, not up). So try and make sure you get the same actual chips.
If you wanted to be sure you could always get the 1GB now, then sell it later and buy a 2x1GB kit. You'd be out a bit more, but you'd be guaranteed dual-channel operation. Up to you.