SQL Server 2008 is available under three licensing models:
Server plus device client access license (CAL): Requires a license for the computer running the Microsoft server product, as well as CALs for each client device.
Server plus user client access license (CAL): Requires a license for the computer running the Microsoft server product, as well as CALs for each user.
Processor license: Requires a single license for each CPU in the operating system environment running SQL Server. This license includes unlimited client device access.
When SQL Server 2008 runs inside a virtual operating environment, it requires at least one license per virtual operating environment, except for SQL Server Enterprise edition.
The Business Intelligence components for SQL Server 2008 include Analysis Services, Reporting Services, and Integration Services. To use any of these components, the server on which Business Intelligence is installed must have a valid SQL Server 2008 license. If these components are in a separate server than the main database server, then they require an additional license of each additional server where they are installed.
For exhaustive information regarding license and price of SQL Server 2008, check out the SQL Server 2008 Pricing and Licensing document.