To hide the extensions, open a window and choose View|Options. Next, click on the View tab (if it isn't already selected). Now select the Hide File Extensions for Known File Types check box. Click on OK to close the dialog box and record your change.

Some file types can cause problems (or at least confusion) when the extensions are not shown. Let's say you'd like Windows NT to display all .TXT extensions. Open a window again and choose View|Options. This time, click on the File Types tab and then locate text files in the list. Click on Edit and select the check box labeled Always Show Extension. Click on OK and then click on OK again when you get back to the Options dialog box.

Now the .TXT extension will appear even though the other registered extensions don't.