XP Pro/SP2.

In the past, when an application needed a Service and the Service was
set to Automatic then it would get launched when needed. Now this
does not happen.

I know some some services are only started when needed (like Perf
Logs And Alerts) but I am referring to services which used to be
started for me in the past.

For example ... if I want to install some software I have to go to
the Services screen and press START on the screen for the Windows
Installer service.

After using it, the system seems to stop that service. So if I want
to install another program then I have to restart it.