click Options > Capture > Start
before you click Start, check the options you want such as foreground window, and how you want to save it.
When you click Start > click to select the window you wish to have in the foreground > Ctrl+F11 (to finish capture)
will put the screen shot in Irfanview or to SaveFile.
2: FastStone Capture
current Shareware version: http://www.faststone.org/FSCaptureDetail.htm
free ver 4.8 http://download.cnet.com/FastStone-Capture/3000-2192_4-10605007.html
This program puts a toolbar on your screen. Choose the type of polygon you want to capture, and save file. The added advantage of this is that one of the capture types is the scrolling window, which scrolls to the bottom of a longer than the screen window to save all of the window.
I use the totally free version 4.8
Current versions will also capture as video.
3. CamStudio Video Capture