here's a link to a program raze once recommended for taking screenshots -
pngshot along with some ideas on parameters should you like -
details this program is quite small and runs easily in the background. it wishes to default to a .png picture, so i recommend changing to the much smaller .jpg format.
to use while in-game simply hit the 'print screen' key.
you'll experience a very slight slowdown of the game for about one or two seconds with each taken pic, dependant upon your system specs.
best of all, it's free!
