(since there are people who are having troubles with it, and upon a request from graywolf, i posted this small tutorial here, hope it actually helps):
find the script you want, mark all of it , right click and choose copy.
Inside rmxp press the F11 button on your keyboard, scroll down the scripts , find main, right click on it and choose insert
you will now have a white line, under it there is a "name zone" type in the name of the script , it can be any name at all (if the scripter asks you to put a name of his choice, do it as it's a way to give the scripter the credit he earned)
move the mouse to the big white zone, right click and choose paste.
the script will now be there and you are ready to use it. (so click ok)