Click on the window that you want to take a screenshot of to give it focus.
Press and hold ALT and then press Prt Scrn.
Open an application such as MSPaint, Photoshop, The Gimp, etc.
Press Ctrl and V to Paste the screenshot. (Alternatively you can go to Edit > Paste)
Click on File and go to Save As....
Save the file as jpg for posting on the Internet.
Distribute your new screenshot!
Note: I used Photoshop for this screenshot so it would look better but not be a massive bitmap file.