In the long run you'll probably either need to find the CD that you used to install Office 2003 or purchase another copy of 2003 or possibly upgrade to Office 2007. However, I've mentioned a possible alternative below the quote.
There are some prerequisites to solving that issue using the information provided in the MS KnowledgeBase using the article When you try to start a Microsoft Office 2003 program for the first time, you receive the "Installation Error: File not Found" error message
To follow the resolution steps in this article, you must have the CD that you used to install the Office program, or you must know the network location from which you installed the Office program. For example, you must have or know one of the following:
* The installation CDs that were included with the software package.
* The repair CD that was included with your computer.
Note This applies only to OEM installations. Computers that are preinstalled with software have repair CDs.
* The network location at your work from which you installed the software. If you are unsure where that location is or how to access it, you must contact a network administrator or your help desk for help.
In the short-term (or possibly the long-term) though you might be able to use OpenOffice
to open the files that you need to access. I would recommend backing up your data files, assuming that they are clean of infections, prior to trying to open them in OpenOffice (just in case). OpenOffice is a free Open Source
alternative to MS Office.
Let us know if this helps. :)
Edit: Looks like I was posting at the same time as a_cup. :)