How about this alternate, wonderfully short paragraph, which borrows the langauge from Perl:
This document is Copyright 2004 by its contributors as defined in the section titled Authors. You can distribute it and/or modify it under the terms of either the GNU General Public License, version 2 or later (http://www.gnu.org/licenses/gpl.html), or the Creative Commons Attribution License, version 2.0 or later (http://creativecommons.org/licenses/by/2.0/).
This version is actually 3 words shorter than the old one. I deleted a redundant "under the terms of" just before "the Creative Commons...".
+1
I like this version very much. It's short, clear, and unambiguous. I also agree that the second "under the terms of" was redundant and should be deleted. Very well done.
Cheers, Jean
