In this post, I summarized how to config VMware Fusion 2's network.

For the new VMware Fusion 3, it's much easier. VMware Fusion 3 has a separate configuration file for networking only. The file is:

/Library/Application Support/VMware Fusion/networking

A sample file as following:

VERSION=1,0
answer VNET_1_DHCP no
answer VNET_1_HOSTONLY_NETMASK 255.255.255.0
answer VNET_1_HOSTONLY_SUBNET 172.16.125.0
answer VNET_1_VIRTUAL_ADAPTER no
answer VNET_1_VIRTUAL_ADAPTER_ADDR 172.16.125.1
answer VNET_8_DHCP no
answer VNET_8_DHCP_CFG_HASH E7EBB6E40048285A05D25835904AFD8BEC1CD2B2
answer VNET_8_HOSTONLY_NETMASK 255.255.255.0
answer VNET_8_HOSTONLY_SUBNET 192.168.42.0
answer VNET_8_NAT yes
answer VNET_8_VIRTUAL_ADAPTER yes
answer VNET_8_VIRTUAL_ADAPTER_ADDR 192.168.42.1

You just change entries accordingly, then do sudo ./boot.sh --restart to active the new config.