Modifying files under Program Files directory in network

Here's a simple question, hopefully, from a beginner. In a simple peer to
peer network in Windows XP how do I grant permission to users to modify
files located within the Program Files directory of a computer. Sharing is
enabled and the Allow network users to change files check box is checked.
Yet, I still receive the no permission error when I try to modify a database
table located in a sub directory of Program Files.

Thanks