Problem configuring ICS in 2003 server

When I try to configure Internet Connection Sharing in 2003 Server I get this error message

A LAN connection is already configured with the IP address that is required for
automatic IP addressing

I presume that it relates to ip 192.168.0.1 but there are only 2 PC's and one router
The set up is

Server network cards
LAN   ip:192.168.0.20     mask:255.255.255.0  
External  ip:192.168.0.21    mask:255.255.255.0    gateway:192.168.0.2(router address)

PC1
PC network card   ip:192.168.0.3    mask:255.255.255.0  running Win XP
PC wireless network card   ip:192.168.0.4   mask:255.255.255.0  disabled
PC bluetooth adapter   ip:192.168.0.10   mask:255.255.255.0

PC2
PC network card   ip:192.168.0.5   mask:255.255.255.0  running Win XP

The server only has the File server Role running at the moment (Still Learning)
I can connect to the internet through the server
I can access the network with both pc's with no problems

Help!