Pop Up Redirect

Hi
I would like to redirect to a page upon clicking the 'ok' button on an 'alert' window
if ($data["data"] == "1")

{

echo "<script>alert('INVALID ENTRY- ')</script>"; .......... How could I redirect from here? Should I use a confirm script or is there an easier way?
}

else
continue with program ..............
could I use the below in the IF/ELSE loop?:
echo '<script language="javascript">confirm("INVALID ENTRY")</script>';
echo '<script language="javascript">window.location = "http://anotherpage.php"</script>';;
Should I use the Header - need to buffer output?
Any help once again appreciated.
Ady