@Raziel
No problem. Write your script to S:ARexx, give it an icon (with start with "ARexx", "C:rx" as standard command), select it WBStartupPrefs. This is it.
The only thing you have to obey to, is to write to the SAME file (read: same file name) every time you write your script. This way your script is started ALWAYS on boot up. If you want to do nothing during startup then you have to write something, that doesn't do anything in your script...