Research Office 64 bit and you'll likely find that it's ill advised for most people, and there are pitfalls if you're developing db's for others who are not on it. Don't upgrade the only 2003 db's you have - upgrade copies and work with those until you're confident everything in it works. Then archive the originals. Upgrading from 2003, you will have an issue with any custom menus or toolbars you created. You will lose the GUI tool that allowed you to create them as well. Some references may break/go missing but you should be able to resolve those. IMO the application windows/forms lack visual appeal to put it mildly. There is always the possibility of running 2 versions if you need it, but you have to know what you're doing with that.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.