Personally, I always just assume that backtracking from unstable or testing to stable isn't practical: The tools and system architecture just aren't really designed to accomodate that sort of reverse upgrade.

Going from unstable to testing is really just a matter of, at worst, changing the /etc/apt/sources.list and waiting a few days -- because, after all, testing is just unstable net of a (usually) brief package-quarantine. Thus, get off the "unstable" track, wait a few days, and resynchronise to testing.

In any event, the drill for reverse-upgrading is [link|http://www.debianplanet.org/node.php?id=880|documented], for those determined to do it. (And yes, all of this is in my Debian Tips file.)

Rick Moen
rick@linuxmafia.com