If you use kde, i suggest you copy your script in /home/dpf/.kde/Autostart (/home/dpf/.kde/Autostart if you use kde4) and make sure your script file is executable .
Yes, or simply right click the file in file manager (konqueror, dolphin, …) and look for something like ‘properties’ and find a check box to tick the executable if needed.
I do not understand this. It is the script that dpff wants to be run. It is in dpfs’ home directory. dpf is the one who made it (I hope). Is not dpf the owner of home/dpf/.kde4/Autostart/<thescript> ? That should be the case. And then no *su *(to root) is needed anywhere! And when root is not needed, it is a major sinn to run as root.