Why and how does Quicktime Player insinuate itself through every program and application on my computer?

Since I've installed Quicktime(6.5 or something like that) it has put its logo through almost every application and program. What's worse, is that when I open some links, I can't play or use the link, because Quicktime has hijacked the correct operation. Files that were previously supposed to play in Windows Media Player, no longer are routed to WMP, same thing with files that normally would have opened in RealPlayer. How do I restore the regular defaults that were on my computer before I unleashed this major pain-in-the-***? There is no setting in the install file to make Quicktime the default player, it just takes over! And I have not yet found out how to push it back into the background! And do not tell me to just uninstall it, as some of the installations are necessary to run some applications, I know because I tried it before! Any help with this would be greatly appreciated,as I am really sick and tired of not being able to run things the way that I used to be able to!