ms office

i have a new laptop that has come with a trial version of ms office 2007. However, I do not wish to stand the expense of a full version at the end of the trial period, but I do have my own version of ms office 2003 and would like to use this.

Bearing in mind the 2003 version was used on XP please advise me how to load up the 2003 version in place of the 2007 version that came with the laptop

Your assistance would be greatly appreciated.