The bug-tracker can be found in the OpenACS repository on the MAIN TRUNK (the development branch), under packages/bug-tracker.
It ONLY runs on OpenACS 4.5 beta, from the tip of the 4.5 branch.
This is a little annoying, but that's how it is.
cvs checkout -r oacs-4-5 openacs-4 to get OpenACS, then
cvs checkout openacs-4/packages/bug-tracker to get the bug-tracker.
(These are not complete cvs commands)