Accountable Students with Computer Use

   When studetns have access in the classroom to use computers on special projects, how can we monitor each student's work?  How can we, as teachers, make sure the students are on task, and not accessing or viewing inappropriate material? 
   As I walked around in one of the classrooms where I am observing students, I found one student was accessing "Lil Wayne" videos.  I don't know how he was able to do this.  It was my understanding that there were security loocks on these computers and search engines.  I asked him to immediately erase and remove the inappropriate material from his computer.  I think I was so flustered that I didn't ask him how he managed to find the material on this computer.
   The 7th grade students were working on PowerPoint projects for different countries.  Most of them were on task.  However, I also found one student had changed the opening screen saver window of the computer and replaced the background with a new picture.  The new picture was the Israeli flag.  There is nothing wrong with the Star of David, however those students who aren't aware of what the symbol represents may take offense to it.  Not only that, but the student could have gotten in trouble for defacing school property.
   In a perfect world with perfect technology, it would be nice to have a visual on the teacher's computer screen of all the students' active computer screens.  This way the teacher would have the accessibility to monitor the progress of the students' work.