Lol wow, great thread.

Step one would be to look into hooking programs. You will want a way to execute commands to the server via your C# app. Hooking it will be required to do so, so I suggest you look into that aspect first.

Also think about how you want the auto messaging to work, every minute? Every time some one joins? Random times (that are above a certain limit), every time map changes? Etc, you need to plan these things out. I have no idea about the H2V server, is there like a say command that he could hook into?