Header Location Question

I have the code below within a larger web page which is like a portal. When I submit the form, I get this message: -------- Warning: Cannot add header information - headers already sent by (output started at c:\apache\htdocs\index1.php3:9) -------- Can I get it to take me to the BigCharts site and leave the page I'm on? Thanks. Jeff Oien -------- <?php print "<form method=\"post\" action=\"$PHP_SELF\">"; print "Symbol<br>"; print "<input type=\"Text\" size=\"5\" name=\"symbol\"><br>"; print "<INPUT type=\"hidden\" name=\"op\" value=\"ds\">"; print "<input type=\"Submit\" value=\"Chart\">"; if ($op == "ds") { $url = 'http://www.bigcharts.com/quickchart/quickchart.asp?symb= . $symbol'; header ("Location: $url"); } ?>