The x.x part is what your computer considers to be on your local LAN - If any other 12. addresses are in that part, you won't be able to see them. Your network admin might have also messed up the router config, too. If that's the case, nothing you will do will make it work. It's definitely messed up, however, so call your admin (or whomever does it) and get them to fix it.
- G