Best How To :

I've made a solution without string parsing...

JSFIDDLE

HTML:

<div id="old" class="old">
    <input type="text" name="id"  size="2" value="1"/>
    <input type="text" name="UM"  size="2"/>
    <input type="text" name="DS"   size="2"/>
</div>
<input type="button" value="Add" id="clone" />
<input type="button" value="remove" id="remove" />

Js

$(document).ready(function(){

var counter = 1;

$("input#clone").click(function(){
    //Let's make a copy to work with
    var originalDiv = $("div#old");
    var cloneDiv = originalDiv.clone(); 

    //Renaming cloneDiv
    cloneDiv.attr('id','newDiv'+counter);

    //Renaming inputs in  cloneDiv
    $("[name='id']",cloneDiv).attr('name','id'+counter);
    $("[name='UM']",cloneDiv).attr('name','UM'+counter);
    $("[name='DS']",cloneDiv).attr('name','DS'+counter); 

    //Value first textfield
    $("[name='id"+counter+"']",cloneDiv).val(1+counter); 

    //Append to originalDiv parent whatever it is...
    originalDiv.parent().append(cloneDiv);
    //OR Append it just after last created div
    //$('.old:last').after(cloneDiv);

    //Increment counter
    counter++;      
});

    $("input#remove").click(function(e) { 
        if(counter > 1){
            //Remove the last clone
            $('#newDiv'+(counter-1)).remove();
            //Decrease counter
            counter--;
        }         
    });  
});