I received an interesting tip this week from Dan via email regarding removing and changing Windows Vista file type associations on the fly. I have to admit, I had never heard of this one:

You can remove a single file type association to more easily reassociate it. (You have to do this under admin rights, however.--Paul)

At a command prompt (cmd.exe) type assoc.file_type= Where file_type is the extension of the file type for which you want to remove the application association. As an example, you could stop PHP files from opening with WordPad by typing assoc.php= and then hitting Enter. The next time you open a PHP file, you will be prompted to choose a program again.

So this does work, but it's somewhat complicated. I recommend using the "Open with" trick instead. This can be used in two instances: When you want to change the association of a particular file type and when you want to just open a file with a different application on the fly. Here's how it works.

Locate the document or other file you'd like to open. Hold down the Shift key and right-click the file. You'll see a new option, Open With, appear. The Open With option will have a sub-menu associated with it. You can choose an option from this menu or select Choose Default Program.

From the Open With window, choose from the list of Recommended Programs. Or, click Browse to find a new program. When you locate a new program, it will appear in the Open With sub-menu and in the Open With dialog going forward. Note too the "Always use the selected program to open this kind of file." It's selected by default, so if you're not trying to change the association, make sure you uncheck it.