Use the Product Key page to validate your instance of SQL Server 2008, or to specify which free edition of SQL Server 2008 to install.
To specify a free edition of SQL Server 2008, select the radio button for free installations, and then use the drop-down box to identify which edition to install.
To validate a paid edition of SQL Server 2008, select the radio button for the Product Key, and then provide your key in the space provided.
For failover cluster installations, use the same product key for each failover cluster node. If the product key is from a different SQL Server edition, an error will occur.