I keep forgetting this simple command and I figured I better just add it to my blog. To print screen on a Windows machine you use the Print Screen button with another button depending on what you are trying to capture. In Windows this puts the image on to the clipboard where you then paste it into the program you want to use to edit or use it. This could be Paint, Photoshop or any number of programs. With a dual monitor or higher setup it is better to just capture 1 monitor at a time otherwise the picture turns out small.
The magic command is Alt-Print Screen which will capture the active monitor. The active monitor is the monitor you click into last.