should do something like this. It also allows people to control your desktop too, but only if you want them to (e.g. password restriction).
This is if you want the client(s) to see your screen exactly as it is. smeezekitty does have a point, though, in that the X window system is network transparent, and you could (in theory) share program usage over the network (or the Internet, but I don't know exactly how one would go about doing it this way).