You don't state:
1. Whether you have administrator rights on the computer in question.
2. Whether you tried the suggestions provided in the error message.
When attempting to check for any needed updates to Microsoft Office XP for Students & Teachers, I get the following error message. This update process used to work for me. I have reported the error to Microsoft, but I do not get any response.
The Office Update site is unable to check for updates on this computer. This may be happening because of one of the following reasons:
You do not have administrative privileges for this computer.
There is a network problem and the detection catalog used by the Office Update site failed to download. Go back to the Downloads home page and try running detection again.
Windows Installer patch files (.MSP files) from previously applied Office updates are missing from the \Windows\Installer hidden directory on your computer. MSP files are stored on your computer after update installation completes because they need to be referenced for future update operations. If the files are missing you will not be able to apply Office updates. You may also be unable to uninstall Office products as a result of the same problem. Please contact Microsoft Product Support for assistance.
You installed Office updates in the past and then upgraded from Windows Installer version 1.0 to Windows Installer version 1.1. For more information see the KB article Windows Installer May Prompt for Install Source if Unavailable.
Search for Office updates in the Download Catalog
Report the error to Microsoft