Given enough time, an incentive to do it, and publicly available software, there is no encryption that cannot be broken. But a simple scheme like yours can be broken a lot faster, probably in seconds. A stronger encryption scheme may take hundreds or thousands of years to break using a PC, weeks or months using a supercomputer.

What are your risks? If security of the data is a high priority you probably should not be using VFP tables, but instead keeping the data on a secure server. Your VFP tables can at least be viewed by many applications, including Excell and Notepad, so having an encrypted password for your application might stop people from using your software to view or change the tables, but not stop somebody from making a modification using Excell.

Security also involves physical security and network security. If there are no controls on who can sit at a computer and get at your files, then encryption is your only protection. An experienced technichian can take a hard drive out of a desktop or laptop in much less than five minutes, and your data is gone.

Security also costs money. Not just the direct cost of the encryption software, but also your program will run slower, less portable etc. Theoretically how much it is worth spending on security depends on the chances of something going wrong times the cost of that disaster. But most organizations do not make very reliable estimates of either of the two inputs, and so either have far too little security or far to much.

I am not a security consultant, but there are people who specialize in this and they can help you objectively rate your risks so that you put an appropriate amount of effort into security.

Hope this helps,
David