Nicolas,
I think you are asking for a way to add more fields to the popup.
If so, you need to change two sections of code.
You need to look at the service and add more outfields for the ones you want to add.
outFields: ["NAME", "POP2000", "POP2007", "POP00_SQMI", "POP07_SQMI"]
and
you then need to add the corresponding fields to this section.
southCarolinaCounties.on("mouse-over", function(evt){
var t = "<b>${NAME}</b><hr><b>2000 Population: </b>${POP2000:NumberFormat}<br>"
+ "<b>2000 Population per Sq. Mi.: </b>${POP00_SQMI:NumberFormat}<br>"
+ "<b>2007 Population: </b>${POP2007:NumberFormat}<br>"
+ "<b>2007 Population per Sq. Mi.: </b>${POP07_SQMI:NumberFormat}";
Can you post the code you have changed so we can see what it looks like?