Using '/' instead of '?' in url querystring

Hi, I wonder if any of you have experience, sending variables in the url without using the ? character. When sending variables this is the normal way to do it: /foo.php?id=12 But I have read that the following URL should work: /foo.php/12/ and then fetch the id in this way: $id = ereg_replace('[^0-9]', '', $PATH_INFO); I have even seen it in function but the problem is that I can't get it to work on my local apache server. When I try to write /foo.php/12/ I get a '500 Internal Server Error' and in the apache error-log I can read that 'Premature end of script headers: c:/php/php.exe'. Does anyone know what could cause this error and why the url isn't working?? thanks Kenni Graversen