1. Start Internet Explorer by double-clicking on the icon on the desktop or by clicking 'Start' and choosing the 'Internet Explorer' icon on the Start menu.
2. Select the 'Tools' menu option, and then click on 'Internet Options.'
3. Click on the 'Programs' tab on the 'Internet Options' dialog box.
4. Click on your desired email program from the 'Email' combo box.
5. Click 'Apply' and then 'OK' to save changes. Now you can use your desired email program as your default email for Excel 2003.