When did you last install Windows

[cro-man]

A hidden utility in Windows XP Pro*, called Systeminfo will also tell you a lot more about your computer, including how long it has been running, what patches and updates have been installed and probably more than you want to know about your computer

[LUZR4LIFE]

Thanks for sharing

[Tarun]

Hidden? This is built in to Windows and it's well known.

Google SIW, it tells you plenty and is freeware.