When choosing between Office 2003 Pro for $55 and Office 2007 Pro Plus for $100, several key points emerge. Office 2007 offers a more modern interface and additional features, particularly beneficial for tasks like entering equations, which can enhance productivity for specific fields such as engineering. However, compatibility concerns arise, as Office 2007 files may not be easily shared with users still on Office 2003, though users can save documents in a compatible format. Many users suggest sticking with Office 2003 to save money, especially for undergraduates who may not need the advanced features of 2007. OpenOffice is also mentioned as a free alternative that supports saving in Office 2003 format. Ultimately, the decision hinges on individual needs for features versus cost, with a general inclination towards Office 2007 for those who can utilize its enhancements effectively.