Windows xp, vista, 7 버전 체크

In XP it contains 5.1, 

in Vista 6.0 

and in Windows 7 6.1 

as you can see here http://msdn.microsoft.com/en-us/library/windows/desktop/ms724834(v=vs.85).aspx.

var ua = navigator.userAgent.toLowerCase();
var isWinXP = ua.indexOf('windows nt 5.1') > 0;