I've had a similiar problem with my home network. Not knowing what the offending computer has been used for I thought it was something worthing checking. If I unplug my workstation from the router and plug it directly into the wildblue modem the registry will be over written. When I plug the workstation back into the router I can no longer reach it from any of my other computers but I can reach them from it. I have to go into the registry and remove a key. After rebooting the computer works fine. Sorry about the lack of detail on the registry key but I have managed to hose my workstation this morning. It is in the local machine/something something/ netbt/ permissions section. Of course last night I erased my workstation backup in order to play around with backing up my new Mac.