I beleive there is a program responsible for launching all the screen saver.

e.g. program flyingwindow.scr

anyone know what program is responsible for it?

What I want to do is use "schedule" to launch screensaver at specific date.

but don't even know what program is responsible for it.

You can launch it just like if it was a normal exe (or you could use a api call or 3rd party app to start the default screensaver too)

if you double click on the file the screensaver runs normally.

but if you type the filename as a command the screensaver properties configuration comes up.

Is there an actual program which is incharge of running the screensaver?

Launch with /s switch

e.g. logon.scr /s

thanx that works with cmd prompt.

but still don't work for scheduled task though, don't knwowhy

This will schedule it using cmd prompt:

at 20:00 /interactive /every:m,t,w,th,f,s,su cmd /c logon.scr /s