I use this method at work, for returning the netbios name of the remote machine:
Get the output of the nbtstat -A 1.2.3.4 command (obviously replacing 1.2.3.4 with $_SERVER["REMOTE_ADDR"]. It'll work on any machine that has netbios running (so pretty much any machine on a local network, except macs :-P)
nbtstat gives you basic information about a netbios computer, such as its name, the currently logged-on user, and domain/workgroup. If you want more in-depth information, check out "psloggedon.exe" from www.sysinternals.com. They have lots more tools which can very easily be used from within PHP, giving you an incredible level of network-awareness 🙂