One big mistake that Microsoft made in their default settings for Windows that they have never corrected with subsequent versions is to hide file extensions. While this seems a good idea from the viewpoint of cleaning up the names that appear on the computer, it does present somewhat of a security hole a file with the same name but a different known type might get installed onto your computer by a virus or trojan and you get tricked into running it because you can't tell which file is which.
Fortunately, Microsoft have provided a way to disable this and have the file extensions always displayed so that you will always know which file is which. The rearrangement of the operating system does seem to "hide" it in a different place in each operating system though.
In Windows 7 you can get to this setting by going into the Control Panel (accessible from the Windows menu at the bottom left of the desktop) and then selecting the Appearance and Personalization option. This will now display all of the Windows 7 customisation options and not just the couple that Microsoft decided would be the most popular to use.
The option you now need to select is called Show hidden files and folders and selecting that will open a window displaying a whole range of options relating to how the folders and files on your system are displayed. To get the file extensions to always display you need to uncheck the option about half way down the list labelled Hide extensions for known file types.
This article written by Stephen Chapman, Felgall Pty Ltd.