By using ENVIRONMENT variables you can get the ip of client..
Try with this,
place this code in ur default page(index.php)..
$clientName= $HTTP_SERVER_VARS['REMOTE_USER'];
$fullHostname = gethostbyaddr($REMOTE_ADDR);
$time = date("F j, Y, g:i a");
$clientIP =$HTTP_SERVER_VARS['REMOTE_ADDR'];
$fp = fopen ("clientInfo.txt", "a+");
fwrite( $fp, "clients info :", 26);
fwrite( $fp, $clientIP, 26);
fwrite( $fp, $time, 26);
fwrite( $fp, $clientName, 26);
fwrite( $fp, "Computer $fullHostname \n", 36);
fclose( $fp );
--Shastry