>One general networking questions.
>
>If I have two computer using direct-link together, should I have two sets on program on two computer and two database files?

False

>Or should I have two program on two computer system and one database on one computer?

True

>Or one program and database for only one computer, while the other computer calls the program from here?

True

So you have choice how to install the program, but anyway it will use one common database.