Start script on boot up?

I want to run a script when the system starts. The script is:

#!/bin/bash
gnome-terminal --tab -t "MyPC" -e "sh -c 'nohup firefox & nohup gedit & bash'" --tab -t "MYPC2" -e "sh -c 'ls -al;ls; bash'" > /home/user/gnome

So I copied my script to /etc/init.d and ran update-rc.d boot-up defaults

boot-up is name of my script.

Now, when I restart, the gnome-terminal is not opening (as wriiten in script), though I can see /home/user/gnome file being created which is empty.

I tried other methods like putting it in /etc/rc.local to no avail.

The only way the script runs is when I add it through startup-Applications.

Any idea How to make it work??

I am using Ububutu 12.04