Lots of different ways to do it. One is by pressing your "Print Screen" key. This will copy an image to the clipboard. You can then switch over to an image editing software window, such as PSP7, and paste as a new image and then return to the sim which will have paused. There are other screenshot utilities out there, FRAPS I think it is for one, that will automatically take screen shots for you and store them in its own folder until you are ready to view them. I think there is a limit on the number in any one session. You can also set the interval between snaps. Its pretty good. Its a sure bet, too, that there are other screenshot utilities that I know nothing about.
Cheers,
MR