This is the FAQ for how to take and save screenshots when you are in the game and you want to take a screenshot of something you think is interesting or when you are pwning and want to take a screenshot showing your score.....
1) Press F5 and take the shot (u can take any amount of screenshots with F5. screenshots will be saved in your "csstrike" folder
C:\Program Files\Counter-Strike 1.6\cstrike
2) hit the Print Screen button on your keyboard, then you minimize the game go into paint and paste it, there you have it the screenshot of your score, after that just click save as.. then the name of the pic.
FYI - For taking a screenshot with your score :
hold down the Tab button so it shows your score...