Demo is available on http://pts.tarantula.fi.
Log in to Tarantula with user accounts:
Username : user
Password : user
Username : admin
Password : admin
For Bugzilla:
Username : user@prove.fi
Password : user
Username : admin@prove.fi
Password : admin
Feel free to explore. There is already some content available on installation.
Database is reset once a day (05:00 UTC), so there is no problem with messing things up :)
You might also want to use walktrough instructions with demo.