Over time, when lots of applications have been installed on a Mac OS X machine, the "Open With..." contextual submenu for files has a tendency to grow to quite an uncomfortable length, especially on older machines, which require a long time to generate and draw it.
One method of shortening the menu is to simply trash the applications you don't use. However, there are many vital applications that are set to be able to open common file types, such as .txt, .avi and .jpg. For example, how often do you open a JPEG file using QuickTime player or Project Builder? but you wouldn't want to trash those apps, either. The following is a way to avoid having these apps clutter your "Open With..." submenu without deleting the apps themselves.
<key>CFBundleTypeExtensions</key>
<array>
<string>txt</string>
<string>srt</string>
<string>suffix1</string>
<string>suffix2</string>
....
and so forth, with the suffices the app is able to open contained within the tags. Then you simply delete the suffix for items you don't want the app to open.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030730161311391