Well it would leave an invalid document because you'd have two elements with the same id, "prod1select". They'd also have the same name so you could have problems when reading submitted data.
That aside the code, in IE, would be something like:
var oParent = Row.parentElement;
var oNewRow = Row.cloneNode();
Although you can change the id of the select after creation you can't change the name so you may want to build your own method of copying the select and then replacing the cloned one with that.
Joe (Microsoft MVP - XML