This problem has been making my life a living hell since we deployed Windows Vista to a handful of workstations several months ago. According to Microsoft,
“Network discovery is a network setting that affects whether your computer can see (find) other computers and devices on the network and whether other computers on the network can see your computer.” What this means to a network administrator is that, even with correct firewall rules in place, communication between your Vista workstations and 2000/2003/XP workstations and servers will basically cease to function. Apparently Windows Server 2008 has a GPO policy that resolves this, but the fact that it hasn’t been released to the public yet tends to keep up from upgrading. In the meantime you can solve this problem by applying a couple of registry entries to your workstations.
[Update]: For those of you fortunate enough to be using Server 2008, check out this page over at the MSDN Blogs about turning on Network Discovery via Server 2008 Group Policy.
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\LLTD] "EnableLLTDIO"=dword:00000001 "AllowLLTDIOOnDomain"=dword:00000001 "AllowLLTDIOOnPublicNet"=dword:00000001 "ProhibitLLTDIOOnPrivateNet"=dword:00000001 "EnableRspndr"=dword:00000001 "AllowRspndrOnDomain"=dword:00000001 "AllowRspndrOnPublicNet"=dword:00000001 "ProhibitRspndrOnPrivateNet"=dword:00000001