CurrentDb

http://msdn2.microsoft.com/en-us/library/aa221178(office.11).aspx

Access
CurrentDb Method [Access 2003 VBA Language Reference]
The CurrentDb method returns an object variable of type Database that represents the database currently open in the Microsoft Access window.
expression.CurrentDb
expression Required. An expression that returns one of the objects in the Applies To list.
Remarks
Note In Microsoft Access the CurrentDb method establishes a hidden reference to the Microsoft DAO 3.6 Object Library in a Microsoft Access database (.mdb).
In order to manipulate the structure of your database and its data from Visual Basic, you must use Data Access Objects (DAO). The CurrentDb method provides a way to access the current database from Visual Basic code without having to know the name of the database. Once you have a variable that points to the current database, you can also access and manipulate other objects and collections in the DAO hierarchy .
You can use the CurrentDb method to create multiple object variables that refer to the current database. In the following example, the variables dbsA and dbsB both refer to the current database:
Dim dbsA As Database, dbsB As Database
Set dbsA = CurrentDb
Set dbsB = CurrentDb
Note In previous versions of Microsoft Access, you may have used the syntax DBEngine.Workspaces(0).Databases(0) or DBEngine(0)(0) to return a pointer to the current database. In Microsoft Access 2000, you should use the CurrentDb method instead. The CurrentDb method creates another instance of the current database, while the DBEngine(0)(0) syntax refers to the open copy of the current database. The CurrentDb method enables you to create more than one variable of type Database that refers to the current database. Microsoft Access still supports the DBEngine(0)(0) syntax, but you should consider making this modification to your code in order to avoid possible conflicts in a multiuser database.
If you need to work with another database at the same time that the current database is open in the Microsoft Access window, use the OpenDatabase method of a Workspace object. The OpenDatabase method doesn't actually open the second database in the Microsoft Access window; it simply returns a Database variable representing the second database. The following example returns a pointer to the current database and to a database called Contacts.mdb:
Dim dbsCurrent As Database, dbsContacts As Database
Set dbsCurrent = CurrentDb
Set dbsContacts = DBEngine.Workspaces(0).OpenDatabase("Contacts.mdb")