create two separate recordsets. one to filter the username column with the username that was entered, the other to filter the IP address column with the $_SERVER["REMOTE_ADDR"] variabel:
<?php echo((isset($_SERVER["REMOTE_ADDR"]))?$_SERVER["REMOTE_ADDR"]:"") ?>
for each recordset, a variable will be created containing the number of rows:
use the Server Validation - number validation
you will need to create one for each the user name recordset, and the ip recordset, use the total rows variable for the server variable and set the minimum to -1 and maximum to 0.
this will cause validation to pass only if both recordsets are empty.