Is there a simple program that can be used to send messages across a network of Mac and PC Computers.

I would just use a Standard IM but sometimes the Internet goes down, which makes communicating difficult plus some computers aren't Internet Sharing Enabled. Also we all use different IM's anyway and I don't fancy signing up to each one.

Just be beneficial if we could use one program, that didn't require any Internet Setup and only relied on sending information to a certain computer not a specific Username via the Net.

I hope I made this clear. Also it's a home network not a business one, there's about 2 PC's, 1 Mac, 1 Xp Laptop and a 360 Connected...Soon to be possibly 2 more PCs and/ or Another Laptop Connected.

So this will just things easier communicating...

Cheers for your help.