That doesn't look like what it says to do on the demo page. Did you test it out?
Once you've put Step 1 from the demo page in the head of your page, it says that you can have as many of these in the body as you like:
<div id="cpcontainer"> </div>
//SYNTAX: myvariable=new dcountup(past_date_and_time_string, "baseunit")
var princewedding=new dcountup("April 9, 2005 13:30:00", "days")
//result is an object containing the current count up date/time, updated every second
//Available properties: result["days"], result["hours"], result["minutes"], and result["seconds"]
mycountainer.innerHTML="Prince Charles and Camilla Parker have been married for: <br /><span class='dcountstyle'>"+result['days']+" <sup>days</sup> "+result['hours']+" <sup>hours</sup> "+result['minutes']+" <sup>minutes</sup> "+result['seconds']+" <sup>seconds</sup></span>"
Black - The parts of the code that must remain unchanged.
Green - These are just comments that tell you what you can do.
Blue - These are things that you will customize as you see fit.
Dark Red - These are the id of the container for the output. Each instance needs one and only one of these but, it must be unique to that instance and used in the two places shown.
Red - These are the variable name that identifies the instance. This also must be unique to the instance and used in the two places shown.