If by chance you are running a webserver on the other machines, you could do something like:
<IMG SRC="
http://othermachine/image.png" border="0" ALT="Othermachine Status" onerror="this.onerror=null;this.src='/offline.png';">
That way, when the other server is online, it will grab the image.png located on that server (just have it be a small image that says "online") But when the server is not up, an error will happen, and it will pull the "offline.png" off of the current server. Optionally, depending on your network connectivity, you might could change the path to the online image to file://\\machinename\share\image.png in the event that you didnt have a webserver running on the remote machines.