doesn't matter that it is with .net, just use javascript as you would normally.
Code:
<html>
<head>
<script language="JavaScript" type="text/javascript">
function MaxWindow() {
  var X = 0;
  var Y = 0;
  if (screen.availWidth){
    X = screen.availWidth;
    Y = screen.availHeight;
  }
 window.resizeTo(X, Y);
 window.moveTo(0,0);

}
</script>
<body onLoad="MaxWindow();">
test
</body>
</html>