First I’m not even sure if Office 2003 is supported on Windows 7. Odds are that it isn’t. Office 2007 is, and Office 2010 is currently in public beta and is.
Try opening the control panel and then the email icon and make sure that you have a data file setup as the default data file.
Uninstalling Office doesn’t remove all the registry keys so each time you uninstall and reinstall you are just removing the files and putting them back.