Ohh.. forgot about the root privs.. /usr/bin/top is just the program top. So if you do like that it will start top on startup. It should work as good as an *.sh script.

I am not sure how you plan to apply it but during the installation you could make the file "chown root:root" and "chmod 755" the file that goes in "/usr/sbin/".

i funny note to this.. when i tried if the above worked i accidentally deleted /etc/init.d/rcS.. luckilly i am doing backups of /etc/* too so i just ssh:ed into my computer and downloaded the backup.