Security has been enhanced in SQL Server 2005. You can not only ENABLE/DISABLE login but can do more then that.

One of my colleague was on vacation so for security reasons I tried to DISABLE his login during the whole vacation, I issued the statement

ALTER LOGIN <login_name> DISABLE
GO

And when he came back, I issued this statemetn to ENABLE again

ALTER LOGIN <login_name> ENABLE
GO

Try doing it, a nice feature.