If you want it to always from now on handle an AVI with a specific AVI handler program, you can right click on the AVI file, and go to Open With-> and select Choose Program, and scroll through all the programs until you find the program you want to always have associate with that file extension type, and check the check box that states "Always use the selected program to open this type of file".
You should now find that all AVI's will run from the program selected. If you selected the wrong one you can reassociate with the correct one.
Hope this helps!
Dave