Down grading office 2007 to 2003?

I recently purchased 2 new systems form dell with office 2007(because they no longer sell 2003). I was told there is a way to down grade 2007 to 2003. We have many applications in 2003 and to maintain consistency we would like to stick with 2003 for the time being. Does any one know how to down grade to 2003? We have the 2003 media from other systems.