This is from MS Knowledge Base. It sounds like several people must have tried to install some part of Office. You can avoid this by NOT using the default installation parameters. MAKE SURE everyone that is administering the program is doing the same thing and installing ALL features to Hard Disk. The other thing I would bet happened is that someone just wanted to use email and didn't understand the difference between setting up a profile and setting up Office as an application/ program. So, if you read below, you just have to fake it out and act as if you are going to install it, then quit the install. This is an annoyance issue for sure.

"Error 25090" error message when you start an Office 2003 program
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Article ID : 827467
Last Review : January 10, 2006
Revision : 1.3
SYMPTOMS
When you try to start a Microsoft Office 2003 program, you may receive the following error message or an error message that is similar to the following:
Error 25090. Office Setup encountered a problem with the Office Source Engine, system error: -2147023836. Please open SETUP.CHM and look for "Office Source Engine" for information on how to resolve this problem.
CAUSE
This behavior occurs when the following conditions are true: • Two people installed Office 2003 on the same computer.
• Both installations were completed by using the AllUsers="" parameter to set the installation for the installing user account only.
• When both people were prompted to remove files that were copied locally at the end of Setup, both people did not remove the files.
• One of the two people removed Office 2003.

RESOLUTION
To resolve this behavior, start the Setup program for Office 2003. To do this, follow these steps: 1. Insert the Microsoft Office 2003 CD in your CD drive or DVD drive.
2. If the Setup program does not start automatically, locate the Setup.exe file on the CD, and then double-click the file to start Setup.
3. After the Setup window appears, cancel Setup, and then respond to the prompts to exit Setup.
Note You do not have to complete the Setup program. Setup fixes the error condition when it is first invoked.