With the release of VMWare Fusion 4 (and its CONTINUED lack of GUI for network manager), I bring you the instructions on how to add networks to VMWare Fusion 4 (now that I can write about it).
In good news, you no longer have to fully restart the network stack via boot.sh, just restarting Fusion will dynamically pick up the changes
All network configuration files are now found in /Library/Preferences/VMware\ Fusion
The networking file contains information about the VMNET's and will be where you do most of your configuration.
For example if you want to create a VMNET4 and have no DHCP and host only networking, you would append to the networking file
answer VNET_4_DHCP no
answer VNET_4_HOSTONLY_NETMASK 255.255.255.0
answer VNET_4_HOSTONLY_SUBNET 172.16.128.0
answer VNET_4_VIRTUAL_ADAPTER yes
Now you HAVE to edit the .vmx of your VM directly.
Something along the lines of:
ethernet0.connectionType = "custom"
ethernet0.vnet = "vmnet4"
ethernet0.bsdName = "vmnet4"
ethernet0.displayName = "Custom Host Only VMnet4"
Special things to note, do NOT use the GUI network selector after you do this and your network will always be grey, don't worry.
If you want to create a NAT'ed network with now DHCP you would do the same as the above, however, the easiest way to set it up would be copy vmnet8/ to vmnet#/ and remove the dhcpd.conf and dhcpd.conf.bak. Edit the nat.conf to have the appropriate subnet and vmnet (also at the bottom you can create port forwarding if you would like). Also edit the nat.mac and update it to something with the same 3 first groupings and change the last three to something unused on your system.