Both my new MBP and 4 years old MB (both running snow leopard) steals other computers hostname every time I connect to the network at work. I use both on 5 different networks at different places and it only happens on one of the networks. They steal a different hostname every time I connect. I found this out by checking terminal, after they discovered that someone got disconnected every time I where there. I am the only mac user using the network and it is a windows-based network with a domain attached that windows users log into.