Was posting all that binary output really necessary? seriously.. that's horrible.
There isn't a problem, GD is generating a PNG format image.. It's a MIME-type issue.
Code:
<?
include("phplot/phplot.php");
$data = array(array('', 10), array('', 1));
$plot = new PHPlot();
$plot->SetDataValues($data);
$plot->SetTitle('First Test Plot');
header("Content-type: image/png");
$plot->DrawGraph();
?>
EDIT: This may be wrong, I just realized you're using some sort of assisting library.. it's probably a configuration issue of some sort, apologies.