Have you tried $HTTP_USER_AGENT?
This should bring back the name of the browser you are using. Once you know the name to look for, you can then begin customising your screens. For example:
if (strpos($HTTP_USER_AGENT,"MSIE")>0) {
// code for Internet Explorer
} elseif ((strpos($HTTP_USER_AGENT,"Blackberry")>0) {
// code for Blackberry handhelds
} ...