limey

I know this is a pretty basic question but I have never dealt with it and so I am a little usure. Any help or suggestions would be appreciated.
I have a friend who wants to install anti-virus protection on his 3 computers at his work. I don't know much about the network he has set up there, but assuming his internal network is based off from a dynamic ip - is it possible to just go out and buy Norton and install the same copy on all 3 computer stations. I guess my question is will Norton allow updates from multiple machines or will he have to look at some kind of liscencing - and if so what kind of expense might this be. Thanks for your help in advance.

Just to clarify - I am not looking to pirate any software or do anything illeagal like that - I am just interested on how I would install an anti-virus program on 3 different staions assuming they're sharing the same Internet connection and what kind of cost might this incur.
Thx.