SQL 2005 Introduces DDL Triggers

Normally you use the trigger functionality with Data Manipulation Language (DML) commands such as INSERT, UPDATE, and DELETE. Now SQL 2005 introduces new Data Definition Language (DDL) triggers. You can use it to audit schema changes.
Example of DDL Trigger:

        CREATE TRIGGER safety 

        ON DATABASE 

        FOR DROP_TABLE, ALTER_TABLE 

        AS 

            PRINT 'You must disable Trigger "safety" to drop or alter tables!' 

            ROLLBACK

        ;        

        DISABLE TRIGGER safety ON DATABASE;  

Please refer to MSDN for details: MSDN: Designing DDL Triggers