For Windows XP and lower you may find this useful, MWSnap3 It is a small program enabling the taking of a screen shot or any part of the screen. Oh and it is freeware.

http://www.mirekw.com/winfreeware/mwsnap.html

For Windows Vista and Windows 7 there is already a screen capture program installed as part of Windows, it is called "Snipping tool" and can be found in the accessories.