You may have noticed, that on any file with a file extension (that’s pretty much anything you can double click on except the default desktop icons and folders), when you try and rename it, it will by default let you rename the actual name of the file and not the extension. This is so that if you have the Hide extensions for known file types disabled, you can see the file extensions. What a lot of people have done, is tried renaming something and forgotten the file extension thus ruining the file until you get the right extension back on it.

If you noticed, if you do have the Hide extensions for known file types enabled, this is the same thing pretty much as you can only rename the file and not the attachment. It’s more of a “safety over your files” really. It also helps people disguising pictures with a .jpg extension as a virus which is actually an .exe extension. Windows Vista is really trying to prevent any damage to your system… unlike previous versions of Windows… *rolls eyes*.