preg_match - help please

Hi I want to see that a user is submiting a form field in the correct manner. So I decided to use preg_match to verify their input. The pattern I am trying to match is; Firstname Secondname I am not bothered about character length just yet (but advise on this would be appreciated if it can be done with a regular expression - saves extra checking code), but I would like case sensitity. The code I haev so far, which doesn't seem to work is; $un = $_REQUEST['name']; $exp = '/^\b[a-zA-Z] [a-zA-Z]$/'; if (preg_match($exp, $un)) { //has this matched? echo "<h2>matched</h2>"; } Help would be greatly appreciated Thanks Steve