Changing the default application on a mac

So as i've been playing with my toy some of files and associations have been a little mixed up. Changin this in windows was easy (maybe cause I'd been on that platform for ages), but on the Mac doesnt matter what I did it never seemed permanant.

Well i've come across RCDefaultApp 2.0.

RCDefaultApp is a Mac OS X 10.2 or higher preference pane that allows a user to set the default application used for various URL schemes, file extensions, file types, MIME types, and Uniform Type Identifiers (or UTIs; MacOS 10.4 only). MacOS X uses the extension and file type settings to choose the application when opening a file in Finder, while Safari and other applications use the URL and MIME type settings at other times for content not related to a file (such as an unknown URL protocol, or a media stream).