First of all, I'm quite sure your desktop has to be a valid server thingiemagig; i.e., it has to allow everyone to access your computer. This will significantly lower your protection against viruses and the like. After that, install Ventrilo s3rv3r and you're done.
Not sure if this is how it works, but this is how I think Teamspeak works, and I heard Ventrilo is practically the same thing.