I have no idea if I'm correct, but as far as I know you just gotta buy an American iMac cable and plug it in to your iMac and it works. I dunno, I'm basing this entirely on the fact that the iMac end of the plugs are the same shape.
Line voltage: 100-240 volts alternating current (V AC) wide range
You are correct
http://docs.info.apple.com/article.html?artnum=30705
...just get the american power cord and that's it.