This, plus a feature to allow a hostonly network to nat out the interface IP of en0 or en1 is necessery. John P.
OK, I think I get this. c789a123's trick simply gets the Mac's built-in natd gateway working, which is why all you have to do is share Internet over some unused port. Then, you configure the guest OS to connect to that gateway, and you're golden.
OK, this host-only networking idea is great. What I think needs to be done is for bootpd to be configured to provide DHCP service for the GuestOSes, so that the address, gateway, and IP server information can automatically be provided to the GuestOS. I think I'm actually going to provide NFS and SMB service over the host-only network, so I can have secure file exchange between host and guest without opening everything up to the Internet.
Easy hack to use Bridged and hostonly together If you use Mac OS X 1.2 or later it's really easy to setup both Bridged and network only. I use Linux as guest but this should be easy using windows also. This is how I did it: 1. Configure your VM using bridged ethernet. 2. Dublicate your bridged mac os x network device in System Prefs... -> Network -> Configure Ports. 3. Give your duplicated interface a static address like 192.168.99.1. (use a network you know you will never get from a dhcp server 4. Boot you guest and give the virtual interface an extra address in linux calles an alias. Fro example: 192.168.99.2 Hope you can use this. Pim