Perhaps, my problem is that I have several instanaces of SQL Server. They are:

SQL Server 9.0.4035 (SharePoint instance)

SQL Server 8.0.2055 (Standard edition)

SQL Server 8.0.760 (MSDE)

SQL Server 9.0.4053 (Express Edition)

The instance with the problem is "SQL Server 9.0.4035 (SharePoint instance)".

If I am using the sqlcmd, how do I ensure I am using the correct instance?

Is the ALTER LOGIN command availble in this instance?