>So it's taken me so long to get back to you. Unfortunately, after examining the VB code, I've determined that it may not be possible to use the DLL from VFP. In researching it, I discovered that some of the function require the address of a callback function. While this capacity is available in VB, it is not in VFP. Sorry.

George,

I studied zip and unzip dll source code.

dllmain.cpp:

// all callbacks are routed through this function
void user_callback( long action, long error_code, long fsize, char *name_or_msg ) {
if ( callb ) { <-- this checks for callback presence

}

Before calling callback, this code checks for
non-zero address.
Since callbacks are not strictly required to work,
you must simply put NULLs instead of callbacks in vfp.
So it must be possible to call zipdll.dll and unzdll.dll from VFP.

Can you give some example of calling those dlls?