ways to add programs to startup in ubuntu by commandline

i've seen several ways to add programs or daemons to startup in Ubuntu 12.04 but I am kind of perturbed with the meaning of each method.
The point of that I am needing is
- A way to run a daemon before login with root as owner
- A way to run a program after the login of one user
- A way to run a program after the login of any user
- A way to run a program when all gnome environment is setted up

Thanks;)

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