Hi!
The os-type of the user will be a part of the user agent string:
$usersw = $HTTP_USER_AGENT;
This is a $SERVER var, not a $POST var, and for Windows/ie it may look like this:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
If you do a match for Windows, Linux et cetera on the result, you'll get the surfers os 😉
kntm