I may be wrong seeing as I don't have the manual in front of me, but I seem to recall that you just hit the PrtScrn key. Barring that, you could install and use fraps to take both screenshots and movies.
The best way I have found to take a screenshot is as follows.
1. focus camera on subject. 2. click on pause button, top left of screen, main menu. 3. press F5 to get rid of all command lines and HUD.
4. press printscreen. 5. press F5 to bring back command lines and HUD. 6. click on pause button again to continue.
The srceenshot will be in the screeshot directory listed by number, you can then rename it to reflect the actual scene. After this I find it best to load the screenshot in to a photo editing program, adjust brightness and contrast, then save it as a .jpg file if you want to post it in the forum.
I have a PM asking about QuickTime picture viewer, so I'll post the detail here for everyone:
The question is - Where can it be found?
I can't actually remember where it is from (apart from Apple - that's a bit broad). After a bit of research, I think it came bundled with the QuickTime player, which is free, or $25 for the Pro version.
Many people already have it, as you need it for some web-features, but otherwise visit here for more detail: http://www.apple.com/quicktime/win.html (Note that there is a different version for Windows and Mac).