I have an Airport network set up with an iMac, MacBook, iBook and two iPhones (at any given time). In the "Shared" section of the Finder sidebar, I can see all the other computers (that are on and connected, of course). On my MacBook, however, I can also see a "PC Server" that doesn't appear on anywhere else. It appears to be identified by a MAC address, but when I check my Airport utility, none of the connected machines show that address. Here's a screenshot. Any ideas?