I try to connect to 2 databases using the following syntax:

$hostname = "192.168.100.***";
$username = "****";
$password = "****";

MSSQL_CONNECT($hostname,$username,$password) or DIE("DATABASE FAILED TO RESPOND.");
//$dbname = "DB1";
//mssql_select_db($dbName, $db2) or DIE("Table unavailable");

$query = "select t1.field, t2.field FROM DB1.dbo1.table t1, DB2.dbo.field t2";

$result = MSSQL_QUERY($query);
echo $number = MSSQL_NUM_ROWS($result);

If i use the commented lines i get the connection to this db but i can't reach the other db but if i don't use them i get a error as follows:
MS SQL message: Invalid object name 'DB1.****.field'. (severity 16) in c:\program\apache group\apache\htdocs\lab\2sql.php on line 25