Which BASIC variant are you using?

In Visual Basic 6, you can either use the Common Dialogs Control (needs a Form) or the dlgobjs.dll that I think is in the Package and Deployment Wizard folder (you may need to register it with regsvr32.exe) to display the standard Windows file open dialog. Obviously you'll have to include whichever one you use with your program, and either an installer or instructions on registering it.

If you're using QuickBASIC/QB, then you'll have to write your own console-based file browser. You could also read the filename in from the COMMAND$ function as part of the command-line arguments - this will let the user drag and drop the file on to your program.

I've not downloaded and tried your programs yet, as I don't have a JJ1 variant to hand (got the Xmas versions somewhere), so do say if I'm barking up the wrong tree here.