This one has been bothering me every time I run Windows Vista; but just haven't taken the time to dig around to find the solution. I like to see my file extensions when browsing through files.
Windows Vista, just as other Windows prior, "hides" known file extensions by default. What makes Vista a little different is that it also does not have the File/Edit/View/Tools/Help menu bar so you are not able to just click on Tools/Folder Options to go to the dialog that allows you to turn on file extensions.
After a bit of internet searching (with no luck), I decided to spelunk on my own to find where this setting is located. It has to exist somewhere, right? I finally found it. Control Panel -> Appearance and Personalization -> Folder Options. Once you click on Folder Options, the familiar dialog is presented allowing you to uncheck the "Hide extensions for known file types" and choose the "Show hidden files and folders". There is a new item added that you might want to check (though I'm leaving it unchecked for the time being) that turns on the File/Edit/View/Tools/Help menu bar for all explorer views. So if you feel lost without the menu, you can turn it on.