Well following David's instructions you can have RealPlayer as the default player for .rm (RP files) & QT for its own files.
Only RP can play/open .rm files since it's one of their own.
Another thing you can do is double check your browser(s) preferences & QT MIME Settings.
BTW: If RP is slowing everything down, then you have something else going on.
Have you tried running fsck since you are still using Panther? See Knowlege Base Article:
http://docs.info.apple.com/article.html?artnum=106214 Using Disk Utility and
fsck to resolve startup issues or perform disk maintenance
If so, suggest that you post the slow down issue over in the forum for your model Mac and/or contact RP tech/customer support.
