In short you can't. But it's very easy to get the same confirmation that you would with a alert box.
1. Pass ID/Email of record along with the delete command, easiest to use a URL
e.g.[PHP] Delete Me[/PHP]
2. On your confirm_delete.php page create two URLs yes or no
e.g.
[PHP]Are you sure you want to delete:
Yes
No[/PHP]
Then on the delete.php page you have some like the following:
[PHP]
if ( $_GET[confirm] == "yes" )
{
mysql_query( "DELETE FROM table WHERE id= '".$_GET[id]."'" );
} else if ( $_GET[confirm] == "no" )
{
header( "location: http://www.yourhomepage.com");
}[/PHP]
Of course this is extremely basic. You would really want to check the variables $_GET[confirm] and $_GET[id] to make sure a hacker wasn't trying to do a sql injection attack on your form. But that's for another discussion. Hope that helps.