most likely you upgraded to WMP 10; it installs that "new" service. It
needs it. Other things comming down the pike will use it too. Leave it on
Automatic. It (really does) make your machine more secure by allowing
properly written drivers to run in user mode rather that system-mode.
Now if your user account is an Administrator type (like 90% of them out
there; 100% under XP Home) it doesn't make much difference, but it's a
step in the right direction.