You may have noticed that the standard "Open..." dialog in Panther is missing the "Go To" field. However, you can use the Shift-Command-G shortcut to display a window where you can enter a path to any directory, e.g. to display hidden Unix directories like /usr, just as you could with the box that's present in Jag.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031019213055945