Permissions for create/alter/drop/execute DTS/SSIS packages in SQL Server 2K5?

Look at the fixed database roles for SSIS and additional SQLAgent roles to manage SSIS packages & SQL agent jobs.
From BOL:
SQL Server 2005 Integration Services (SSIS) includes the three fixed database-level roles—db_dtsadmin, db_dtsltduser, and db_dtsoperator—for controlling access to packages. Roles can be implemented only on packages that are saved to the msdb database in SQL Server. You assign roles to a package using SQL Server Management Studio. The role assignments are saved to the msdb database.
SQL Server 2005 introduces the following msdb database fixed database roles, which give administrators finer control over access to SQL Server Agent. The roles listed from least to most privileged access are:

• SQLAgentUserRole
  
  
  • SQLAgentReaderRole
    
    
    • SQLAgentOperatorRole
      
      

• • When users who are not members of one of these roles are connected to SQL Server in SQL Server Management Studio, the SQL Server Agent node in Object Explorer is not visible. A user must be a member of one of these fixed database roles or a member of the sysadmin fixed server role to use SQL Server Agent.