Viewing File Extensions
(Windows only)
Open Windows Explorer
Start, Programs, Accessories, Windows Explorer.
Click View, Details from the main menu.

Click on Tools, Folder Options and choose the View tab. Make sure the check box next to "Hide exensions for known file types" is unchecked. Click OK. Now all the file extensions will be visible.

If you want all folders to do this, click the button Apply to All Folders. If it gets messed up, the button Rrestore Defaults is at the bottom.

Some common file extensions are:

*.xls Excel file
*.doc Word file
*.mdb Access file
*.txt Text file
*.jpg, *.gif, *.png Picture files
*.exe Executable file
*.cpp C++ source file