I just use the unregistered version of FRAPS (
http://www.fraps.com/ ) if I want full screen screenshots . Just set the key you want as your ' shutter ' key and then you can take as many pictures as you want without coming out of the game ( I just use the Print Screen key as my camera key with it for convenience ) . You can also use FRAPS to benchmark how fast the frame rate is if you think your game is ' stuttery ' when you move the mouse around . And you can also use it to make videos of your game ( although if you want large , quality , lengthy videos with it you need to pay to register it . If you just want it for screenshots though the unregistered version works fine
To use FRAPS with your game it's as simple as just starting up FRAPS and then starting up your game while FRAPS is running . You say your new comp is a monster so in theory you should be able to always run it in the background while your game is running