Just a guess, but I don't think you want the ($j) in the function
call. I think you're redefining it twice. I think it should be this:
$j = jQuery.noConflict();
$j(document).ready(function(){
var plot1 = $j.jqplot ('#chartdiv',
[[3,7,9,1,4,6,8,2,5]]);
});
But I haven't tried it.