problem with office 2003?

Might be that the uninstallation of Office 2007 was not thoroughly cleaned. Did you reboot your PC prior to installing Office 2003, or right after uninstalling Office2007? Because of original office files were linked to be opened with Office2007, that's what the error message is telling you. The start-up is still looking for Office2007.

Use regedit, if your comfortable with it, and verify if Office2007 still exist in the registry. Use either MSECUI or CCleaner to clean the registry of Office2007. Once Office2007 is purged from the registry, try reinstalling Office2003.

Another perceived problem is the version of your Office2003 installer, if you are installing Office 2003 Basic Edition it is an OEM-only edition, meaning it should have come pre-installed by the computer manufacturer, and you cannot install the software on a second computer or transfer the software to another computer. Either get a Office2003 Home or Prof.

Another suggestion try disabling your antivirus/antispyware applications is when you re-install Office2003. This might be also the cause that the Office2003 over Office2007 installation was corrupted because your antivirus/spyware application could have protected the registry with the Office2007 entries from being overwritten by registry entries for Office 2003. Disabling the antivirus/spyware could trick your OS that your are deliberately installing Office2003 over Office2007, and that it is not a malware that is trying to supplant Office2007 registry entries with that of Office2003.