You want to change the default application for a certain type files?

There are two onboard ways of changing that, I know of:

• get into the information dialog of a file of the given type (right click the file)
• select your favorit application in the "Open with" section
   
• click the "Change all" button

OR

• again right click the file of given type
• hold down the ALT-key
• "open with" will change into "always open with"
• select the program you want  

If this looks to complicated to you have a look here at RCDefaultApp.