>UI - communicates with business layer and users (Presentation)
>Business layer - it's middle layer, it's between UI and Data layer (Business Logic)
>Data Layer - it only communicates with Data Storage (DataBase)

In your design the ADO commands would be in the business layer because your design places the responsibility of fetching and posting data in that layer. You may use different classes of objects to handle the different ways to talk with the data storage layer. By using classes you can have one section of the business layer that uses ODBC to access the data while another area uses ADO by simply deciding which class to instantiate. If you make the classes all subclases of one abstract business class then the interface to the classes will be the same regardless of how they go about talking to the databases.