you can use a dictionary to achieve this. eg-
var dict:Dictionary = new Dictionary;
for(var num:int = 0; num< 2; num++)
{
var str:String = "nWin"+num;
dict[str] = new nwindow();
dict[str].width = 320;
dict[str].height = 200;
dict[str].title="window" + num;
dict[str].open();
}