VNC + a reverse form of remote install OS X

I have set up VNC to open at boot without the OS being logged in by doing this.

Now I am trying to figure out if I can set it up to screen share on another mac without booting into the system. I am trying to basically remote install OS X on my big imac from my little imac. The big one has 10.6 on it (4 month old 27" mid 2010). The little one has 10.5 (non Intel white G5).

I have to use either VNC with the ability to screen share or some form of remote install os x (in reverse form) without booting OS X and only working from the startup screen that appears when you put the disk in and reboot to install OS X. I was going to target disk mode, but that also requires me to use the computer screen that OS X is being installed on doesn't it? I have to do this completely remotely since I can't see the screen until booted into OS X and mirrored to my external. I was unsure if the Firewire 800 on the 27 and 400 on the G5 each would be an issue since they are different.

This complicated situation comes from the fact I cannot force my iMac to use the external display if the system is not booted into OS X and is only at the start screen, and my iMac screen is faulty hence making me use the external display.

So....... iMac needs to reinstall OS X, cannot because install screen uses main display, have enabled VNC at boot, but no way to screen share that I know of without booting OS X completely up rather than being at install screen.