In Mac OS X 10.3's Finder, the toolbar widget (or View -> Hide Toolbar) not only hides the toolbar, but also the left pane.
For the people who would like to have the toolbar but not the left pane, do not despair yet! You can simply double-click on the resize dot separating the left pane from the main content area to collapse the left pane. However, this works on a per-window basis, so you'll have to double-click for every new window.
Note that the same technique can be used to bring back the left pane back to where it was.
[robg adds: I'm not aware of any way to get the opposite -- hiding the toolbar while still having a sidebar. Also, as in previous releases of OS X, you can make the "with toolbar without sidebar" appearance the default for all new windows with this method: Close all Finder windows, open one new window, double-click the dot to vanish the sidebar, set any other settings (view type, size, position) that you wish, then close the window before activating any icons within the window.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030929124312818