Welcome to WebmasterWorld Guest from 22.214.171.124
Forum Moderators: open
 Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:126.96.36.199) Gecko/20060508 Firefox/188.8.131.52
 Opera/9.00 (Windows NT 6.0; U; en)
 Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 6.0)
For FF1.5, Opera9 and IE7b respectively. The presence of "Windows NT 6.0" in each case should indicate Windows Vista.
But beware that user agents can be faked, so it's not 100%, but I don't think there is anything better?!