In January 2008 I purchased a Dell Inspiron 530 (Vista) and had MS Office 2007 Professional loaded on it. I am currently enrolled in a MS Office certification class and the class works with MS Office 2003. I would like to download my exercises from the course, but in doing so they obviously download in the 2007 version. If I purchase MS Office 2003 and download will it override the MS Office 2007 I had installed? Can I later re-install 2007 with the disc that came with my computer?