One old school Quark troubleshooting trick/technique was to create a Preferences folder within the QuarkXPress application folder, which Quark would magically see and create it’s preference file there instead of in the ~/Library/Preferences folder. Apparently this technique isn’t compatible with Snow Leopard, and it can cause Quark to crash at launch. If you are troubleshooting a problem where Quark won’t open, check to see if this folder exists, and delete it if found: /Applications/QuarkXPress/Preferences.