Connect Firewire cable from G5 PowerMac to iMac

I am having problems with my graphics card on my G5 & want to hook it up to the iMac so that i can re=install everything. When i start up the G5 it turns on but it won't open on the imac. at the time I am turning on the G5 what do i do to the imac?

does this make sense to anyone?

thanks