One of the best new features in OS X is the ability to batch-convert application links for various documents. Before finding this, I had inadvertently started up Classic simply by clicking on a .jpg file that could have been viewed in Preview instead. To make the files open a different application, shift-click to select as many of the same document type as you want (for example, 100 .jpg files), then choose Show Info from the File menu in the Finder. Select Application in the pop-up menu and you will be able to select any application you wish to open the files. Once you've made your choice, the batch-conversion is nearly instantaneous.