As a gentle reminder, Exchange 2003 SP2 introduced extra storage space for the data store. The configuration is now as follows:
You can configure a logical database size limit for each of your Exchange databases. The logical size of the database equals the physical size of the .edb file and the .stm file minus the logical free space in each. The limitation of this feature depends on the version of Exchange Server 2003 you are running:
Exchange Server 2003 Standard Edition By default, the size limit of each database on a server running Exchange Server 2003 Standard Edition is 16 GB. After you install Exchange Server 2003 SP2, the default size limit for each Exchange database is 18 GB. Additionally, you can configure database size limits of up to 75 GB for each database on servers running Exchange Server 2003 SP2.
Exchange Server 2003 Enterprise Edition By default, the size limit of each database on a server running Exchange Server 2003 Enterprise Edition is 8,000 GB. This size is generally a theoretical limit. The actual limit of an Exchange database is based on your server hardware and on the hardware of your storage subsystem. After you install Exchange Server 2003 SP2, you can customize the database size limit to a value up to 8,000 GB.
Further details can be found here at the micorsoft website.