Running Ubuntu 10.04 LTS, we were seeing an error in trac (File js/jquery.js not found) about jQuery being missing.

After plowing through about 20 forums, I finally found a post which gave a tip similar to this:

ln -s /usr/share/pyshared/trac/htdocs/js/jquery.js /usr/lib/python2.6/dist-packages/trac/htdocs/js/jquery.js

After doing that, jQuery showed up.