Thanks. The problem I'm describing occurs when using IE 6. Our classrooms have only IE 6 at the moment because of other software constraints (We have an eLeanring system that does not support IE 7 yet in production).
Everything works fine with IE 7 and Firefox, but again we can't use it in our computer classrooms.
It terms of configuration, we're using a WIN SERV 03 with latest versions of PHP.