A. A. SQL has three services
The MSSQLServer service controls if the SQL Server is running and allows logons/transactions. The SQLExecutive service is used for alerts, scheduling and other management tasks.
MSDTC is the Distributed Transaction Coordinator and is used for consistency between server transactions and is beyond the scope of the FAQ.
These services can both be stopped/started from the Services control panel applet and you can also configure them to automatically start at bootup time by selecting one of them, clicking Startup and set to Automatic. Repeat for the other service.
To stop/start from the command line use
C:\> net stop MSSQLServer
C:\> net stop SQLExecutive
C:\> net start MSSQLServer
C:\> net start SQLExecutive
SQL actually comes with its own service manager (Start - Programs - Microsoft SQL Server 6.5 - SQL Service Manager) which enables you to start/start/pause (pause is not available for SQLExecutive) services on various SQL machines. It also shows the current state of the services in a traffic light, ahhhh :-)