How to shut down a computer having a particular IP address?

If we have a collection of Windows and Linux computers on a LAN, is it possible to shutdown a computer having a specific IP address, using the Linux shell?

Assume that I do not have ssh or telnet running on the PCs. I have the root password for all the computers.

Just to give you an answer based on your question: "Shutting down a pc based on just the ip address is impossible"

You can make it possible by making their desktops or shells available over the network. RDP(windows) / SSH or VNC (linux) will do.

Use out-of-band cards (if the computers don't already have them).

They're not cheap cards, but you assign an IP address to each card and you can remotely power cycle/connect/kvm anything really.