In Vista, use the snipping tool.
* Click on the windows button in the menu bar (lower left).
* Type snip in the search box at the bottom.
* Click on snipping tool.
* Select the part of the screen you want to capture by clicking and dragging.
* Click the disk icon to save.
In XP, use MW Snap:
*After installing it, you start the mw snap application and then click on whatever you want to take a picture of and then click back on mw snap.
* click on "any rect area" (if you want to only take a shot of part of the screen)
* click on "snap window".
* click on upper-left corner of what you want to grab.
* make rectangle the size you want and click again.
* click on disk icon to save it.