chat help

I wanted to make a new chat system where you could talk to people privately. I was going to use it in a map I am making, the only way I could think of was the Diablo II chat method using !'s. I can make it so when you type it will create floating text above your characters head with your name attached, and no text will show up in the chat log. How do I make so that either noone be able to see the text I type with a ! in front of it, or so when I type text with a ! it will wipe the screen?

Any help would be appreciated.

Thanks.