"File Type" associations are the links between your documents and the applications that create them. For instance, when you double-click a Microsoft Word Document on your desktop, Windows knows to start Word and instruct it to open the document because of the Microsoft Word Document file type. Likewise, when you click a website link in an email message, Windows knows which browser to open (e.g., Firefox, Internet Explorer) because of the HTTP Protocol file type.

The Folder Options window in Windows Vista is missing the File Types tab found in earlier versions of Windows. So how do you edit file type associations in Windows Vista?

There are three ways:

Method #1 (on the fly):

1. Right-click a file of the type you want to change, and select Properties.
2. In the General tab, click the Change button.
3. Choose a program from the list, or click Browse to select an .EXE file on your hard disk.

Method #2 (view a list of file types):

1. Open Control Panel.
2. In Control Panel Home, click Programs, and then click Make a file type always open in a specific program.

   Or, in the Classic View, open Default Programs and then click Associate a file type or protocol with a program.

3. Highlight a file type in the list and click Change Program.

Unfortunately, neither method in Vista allows you to choose anything but the default programs, such as the programs listed in your files’ context menus. If you want complete control over your file types, use this tool:

Method #3 (File Type Doctor):

1. Download and install Creative Element Power Tools.
2. Open the Creative Element Power Tools Control Panel.
3. Turn on the Edit file type associations option, and click Accept.
4. Right-click a file of the type you want to change, and select Edit File Type to show this window:

Source: Annoyances.org