the volume licensing is only 1 copy, licensed over as many machines as you have (£46 per machine roughly). however the os comes in DVD format not CD, therefore the older macs we have (iMacs and early G4's) which have no DVD drive, cannot have the new os installed. you cannot install from external DVD drives and Apple said they just cant help.
they dont support their older machines apparently.
believev me this is legit, if you can help i can give you my university email address where you can email me privately if you are concerned about the legalities of the situation.