How can i run shell script at boot (start up)
echo /path/to/script.sh >> /etc/rc.local
As dyasny said, you can add the script call to your /etc/rc.local.
Another (cleaner) way would be to write an init script for it, place it in /etc/init.d/yourservice and add rc links to it (I don't remember which command does that on RHEL5) so that it gets started in the right position during boot and stopped during halt (if necessary).