Yes, you must assign a static IP to the NIC of the machine that will do
the ICS. Use 192.167.0.1 for the ICS machine's IP and a netmask of
255.255.255.0
The other machines can be static (as long as they use an IP between
192.167.0.2 thru 192.167.0.254, 255.255.255.0 for netmask and
192.167.0.1 for the gateway address) or automatic IP. Sometimes static
seems to work better that auto, sometimes not. I've had them set to
static, they work fine, next reboot they don't, so I set to auto, then
it works. Don't know why. Probably more to do with Windows cacheing
network info more than anything else.
I know of no other way to do ICS (also called IP Masquerading in case
you want to search for more info on the web).
Steve