[Phanx]

1. Create a folder within your AddOns folder called "AutoGuildMessage".

2. Create a file within that folder called "AutoGuildMessage.toc" and put this in it:

## Interface: 20003
## Title: AutoGuildMessage
AutoGuildMessage.lua

3. Create a second file called "AutoGuildMessage.lua" and put this in it:

SendChatMessage("Your message here", "GUILD")

Note that I'm not at home right now, so I can't test this, but it should work. Let me know if not.

Edit: If you want to be able to change the message from in-game that wouldn't be hard to add...