You are unable to check updates for Office 2003; neither can you repair or reinstall Office.

From Microsoft Tech Support (Hotfix)

Your operating system is Windows XP.

To fix the problem, try the OUCPR.exe tool to see if it is of help.

Run Repair tool to repair the Windows installer files

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1. Save the attachment (OUCPR.zip) to the desktop and unzip it.

2. Rename the file OUCPR.ex_ as OUCPR.exe.

3. Double click the file OUCPR.exe.

It checks out the problematic MSP files, please click Unregister button to fix the issue. This will unregister the existing service packs/hot fixes from the windows installer. After unregistering, try running the service pack again or hotfix.