It’s worse than I thought previously. In this latest version of QuickTime, even if you configure QuickTime not to associate itself with various file extensions and MIME types, it ignores it and associates anyway.
To forcibly remove the QuickTime associations with file types you don’t want it to be associated with, run the program that you want associated with the file type (eg Winamp, Media Player Classic or whatever) and associate it from that program. Then be sure never to start the QuickTime player, or you’ll have to do it all over again.
This is really stupid. Hasn’t Apple learnt its lesson? These are the things that made QuickTime and Real player a bane to computer users, making many avoid these players.