Stop a screen saver from a service

I'm running a service, which does some processing. I only want to run this
processing when the system is not busy (e.g. <5% cpu usage). If the screen
saver is running, is there anyway I can send a fake key stroke to the screen
saver desktop to cancel it form my service? On top of that, is there a way
to detect if a screen saver is actually running forma service? I can't
access the registry as I don't have access to the users HKLU?

TIA

Mat