Mac OS prior to OS X
To determine the version of a program you are running on a Mac, launch the program, then click on the Apple menu and select the first item in the menu, ‘About program name’. This will give you basic information about the program and it’s version.
To see more detailed version information, find the application in the finder, click the program once to select it, then choose ‘Get Info’ (through OS 9.x) or ‘Show Info’ (OS X and above) from the File menu.
Mac OS X
With the program running and the top application, click on the programs menu which is located to the right of the Apple menu. For instance, with Mail running, the menu to the right of the apple will be ‘Mail’. The first item in the menu will be, ‘About program name’.