I don't know if this has been addressed, but I noticed that you can hide/show the Sidebar in a Finder window with this key combination:
Control-Option-Command-T
[robg adds: The Finder's View menu shows Command-Option-T, which hides the Toolbar and the Sidebar, but I can't find any mention of this method of hiding just the Sidebar. I also don't know if it works on 10.3 -- if someone can test it, please comment. For now, I have not marked it Tiger-only...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050516211940586