Some new SQL 2005 functions in tSQL here. Note the cool ability to rename SA to something else!
/*
Disable a login
Rename a login
*/
ALTER LOGIN sa DISABLE;
Select * from sys.sql_logins
ALTER LOGIN sa WITH NAME = [sys-admin];
Select * from sys.sql_logins
ALTER LOGIN [sys-admin] WITH NAME = sa;
Select * from sys.sql_logins
ALTER LOGIN sa ENABLE;
Select * from sys.sql_logins