Editor's note: REVISED ARTICLE to reflect info from Apple's Knowledge Base.
I wish I had visited OSX Hints earlier ... I asked friend of mine, who I've trusted to always give me good advice, how I could get sendmail working on my TiBook. He said all I needed to do was type (in the Terminal) sudo chmod -gw /. Instead of this, I highly recommend this hint offered by jpbjpbjpb - it doesn't turn your disk into a read-only disk! Ok, well to be fair, we both had a few pints to drink that night.
If you you ever end up in the same situation, You can regain control by starting up in single-user mode (apple-S on startup), and when you get the command prompt you can type the following:
% mount -uw /NOTE: This information was taken from Apple's Knowledge Base, article number 106464.
% chmod 1775 /
% reboot
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020528090350838