Nancy, are you a representative from VMWare?
Here are some details:
My Mac (host system) is on a private network at my house: 172.20.204.0/24, it's IP address is 172.20.204.12. My DHCP/DNS server is a Windows 2008 server at 172.20.204.2. My screenshot may be a little confusing because it shows my Windows 2008 server as having a VMware MAC address -- that's because it's a virtual machine running inside of an ESXi server 
My Windows 7 VM has two network adapters configured -- one NAT and one Bridged. I always prefer to use NAT because sometimes I'm VPN'd in on my Mac and want my Windows 7 VM to be able to reach VPN-based systems. I normally leave the Bridged network device as "disabled" within Windows 7. I don't think it matters, but I configured a custom network range for the shared NAT network between my Mac and NAT-enabled VM instances (172.31.255.240/28) - as you can see it is different than my home network range.
I start seeing a flood of NBNS queries emanating from my Mac's IP address (172.20.204.12) and destined for my DNS/DHCP server (172.20.204.2) after using my Windows 7 VM for a certain period of time. I haven't been able to narrow down exactly when it starts -- or what might be the trigger event that starts the flood. I run LittleSnith and I usually notice the problem when I see LittleSnitch's network graph start getting pegged with traffic when I have no other significant network activity going on. If I suspend or shutdown my Windows 7 VM, the traffic continues. The only way I can get the NBNS flood to stop is to manually kill the vm-natd process and start it again by hand (via sudo). Sometimes when I try to restart it, I get the following error:
7/4/13 10:54:47.889 PM vmnetNAT[16148]: Reporting status to parent on status fd: 7 failed, error: Device not configured
As a side note, can you explain in detail what these settings in vmnet8/nat.conf do?
[netbios]
# Timeout for NBNS queries.
nbnsTimeout = 2
# Number of retries for each NBNS query.
nbnsRetries = 3
# Timeout for NBDS queries.
nbdsTimeout = 3
I haven't fiddled with any of these defaults...maybe they are related to this problem?
-Arion