Testopia is a full featured test case management extension for Bugzilla.
Version 2.4 (Bugzilla 3.6/4.0) and Version 2.5 (Bugzilla 4.2/4.4) are available from FTP.
Be sure to read the README for installation and upgrade instructions.
Testopia 2.0 and above NOW REQUIRES JSON 2.10 You will need to update to the latest version of JSON from CPAN. Also recommended is JSON::XS which will boost performance.