This Microsoft article describes the use of the FileDialog method to show a select file dialog.
The FileDialog object is new (introduced with Access 2002). It is an alternative to the Common Dialog Control (which may not be available to you depending on your licensing) and the File Open/Save API (which is the generally recommended solution on the boards these days).
The FileDialog object doesn't work with the runtime version, and it requires a reference to the Microsoft Office library, but for my money it's simple and clean to code and it fits my needs.
Also note that the FileDialog method can be called from other VBA hosting applications, such as Word or Excel, with no changes becuase it's part of Office, not part of Access.