Timothy,

You can append from a file that is currently open by another user as long as that user does not have the source file opened exclusively.

Be sure in your tests that you open teh source file as SHARED before you try appending from it in the other session.

Yes, two instance of private data sessions in VFP simulates a multiuser environment. It does not completely match though as there is no network stuff and no cables that might get loose or anything like that in the situation, but for file contention it is a valid test scenario.