start VINO at boot

I need to give remote assistance to my users, I need to let them watch what i do on their computers.

I wish to use free software (I heard about Real VNC but i know it must be paid for business)

I need that VINO is started at boot time, before user login, in order to allow me to see the login prompt, and choose to login as user1 or user2.

Local users must watch what I do on their computers.

I tried vnc-server but i've seen that windows opened on remote connection are not shown on local display. Moreover, with vnc-server I couldn't setup a remote login before a user was logged in.

For these reasons i suppose VINO should be the right solution. Did I said something wrong? Do you know how to setup VINO for this purpose?

Thank you.