Seeing the same symptoms here, constant NetBIOS chatter while Windows 7 is running within VMWare Fusion 5.0.3. Disabling NetBIOS within Windows 7 as per previous post didn't help. Looking at /Library/Preferences/VMware Fusion/vmnet8/nat.conf if I bump up the netbios-related timeouts to 20 seconds:
nbnsTimeout = 20
nbdsTimeout = 20
then indeed I see the busts of NetBIOS packets directed at our domain controller (which doesn't answer) only every 20 seconds, which helps to reduce the traffic, but doesn't eliminate the problem. It may be that the problem is also on the domain controller / active directory side, which would cause the domain controller to ignore these WINS queries?