You mean like the following keys on my keyboard:
= Back
= Forward
= Stop
= Mail
= Search
= Favorites
= Web/Home
= My Computer
= Calculator
= Sleep
Well, those keys are not "Standard" keyboard keys. They are manufacturer keys, that can be programed with software that accompanies the keyboard, or the computer itself.
However, yes, it should be a key on the keyboard. It's located once or twice on the keyboard on the bottom, close to the spacebar.
Things like Windows Key + Pause/break will bring up the system properties. Windows Key + R will bring up a "Run" command window. Windows Key + E will bring up a windows explorer window, and several others.
Don't know if that's what you mean by a, "windows Button" though.