Here is a write on changing windows file type associations from:http://pcsupport.about.com/od/fixtheproblem/ht/default-program-windows-7.htm
Follow these very easy steps for changing the program that starts when you open a particular kind of file in Windows 7.
Click on Start and then Control Panel.
Tip: In a hurry? Type associations in the search box after clicking the start button. Choose Make a file type always open in a specific program from the list of results and then skip to Step 4.
Click on the Programs link.
Note: If you're viewing the Small icons or Large icons view of Control Panel, you won't see this link. Click on the Default Programs icon and then click on the Associate a file type or protocol with a program link. Then proceed to Step 4.
Click on the Make a file type always open in a specific program link under the Default Programs heading.
In the Set Associations window, scroll down the list until you see the file extension that you want to change the default program for.
Click on the file extension to highlight it, once you've found the one you're looking for.
Click the Change program... button above the scroll bar.
The Open With dialog box should appear.
Look through the options in the Recommended Programs area and choose the application that you want to open the file extension with when you double-click on the particular kind of file on your computer.
Note: Chances are, the applications listed under Recommended Programs will contain the most applicable programs for this file type but be sure to look at the applications under Other Programs. You may need to click the v to expand the list of these programs.
Note: Click Browse... to search through your computer for any program not listed that you'd like to use.
Click the OK button on the Open With window. Windows 7 will refresh the list of file associations to show the new default program to open this type of file.
Click the Close button at the bottom of the Set Associations window. You may also close the Control Panel window if it's still open.
From this point forward, when you double-click on any file with this particular file extension, the program you associated it with in Step 7 will launch and load the particular file.
Important: Whatever program used to automatically open when these types of files were launched will still open these types of files. To use another program, you'll just need to start the program manually and then browse your computer for the particular file.
Not a Windows 7 user? See how to change the default program for file types in other Windows operating systems.