Oracle ODBC connection Problem

i'm trying to connect to a oracle database using the odbc driver with the followin script: ---------------------------------------------------------------------------- --------- <?php $user="user"; $upasswd="password"; $dsn = "dsn"; $query = "select sysdate from dual"; print "<p>query is: <code>$query</code><br>"; $conn = odbc_pconnect($dsn, $user,$upasswd ); if (!$conn) { print "Connection failed\n</html>"; exit; } if ($result = odbc_Exec($conn, $query)) { print "Query returned : " . odbc_num_rows($result) . " rows"; odbc_result_all($result, "border = 1"); }?> ---------------------------------------------------------------------------- ---------and received the following error: Warning: SQL error: [Microsoft][ODBC driver for Oracle][Oracle]ORA-12154: TNS:could not resolve service name, SQL state 08001 in SQLConnect in c:\php\files\p.php on line 11how can i make this script work perfectly?