How about :
$query = "SELECT * FROM {$username}";
$result = mysql_query($query,$connection);
if ($result !== FALSE) {
print("Sucsess, table {$username} found");
} else {
print("Failure, User not found");
}
It tries to find that table, if it fails the error is suppressed with the @ and the if statement prints out an error if needed.
is there any reason why you have a table for every user instead of a members table with each user as a row?