Sorry for not replying since yesterdaygot some stuff on my mind here.
Well, the truth is, Quickbooks is not an everyday application everybody has experience on(atleast, I don't

).
I understand what you are tryin to do but you have to understand that you need to provide more information:
1 - Is the application web-based or simply a desktop application.
2 - Does it natively support multi-user with simultaneous log in?
If you answer NO to #2, then its not possible to achieve what you want. because, only one of the intended 5 users would have access to the software no matter what you do!.
In short, read the manual of the application. If it has support for multi-user(client-server scenario), it's setup would be clearly stated. That way, user's you want to give access to would just be assigned a profile.
Otherwise, its going to be almost impractical to achieve what you desire.