You have to do this in the briefing with the briefing.html, or maybe a similar file. There is a tool with a wizard that lets you do stuff like this (this included) on this site called the Operation Flashpoint Mission Assistant. I think that's the name, but I may be wrong. It will guide you through briefing.html, inet.sqs, and one other, I think.
8)This tool is very handy and saves you a lot of time.