This is from the Black Viper's site for XP.
Remote Procedure Call (RPC)
"This service is rather vital. Practically everything depends on this service to be running. This is also the only service that you cannot disable via the Services MMC. Previously, if you disabled this service in Windows 2000, your computer would become unbootable. What I am trying to tell you is leave this service on automatic and absolutely DO NOT disable it. If, for whatever reason, the service became disabled and you can no longer boot your system, please read the information here for a way to fix it."
"I disabled Remote Procedure Call (before I read your advice) and my computer is broke! What do I do?"
http://www.blackviper.com/AskBV/2k4.htm