rmarshall 
I give you more detailed info about the configuration of sme server:
Server Mode   servergateway
Local IP address / subnet mask   192.168.0.100/255.255.255.0
External IP address / subnet mask   192.168.1.2/255.255.255.0 (connected to router)
Gateway   192.168.1.1 (that is the router)
Additional local networks   192.168.0.0/255.255.255.0
DHCP server   enabled
DNS server   192.168.0.100
I'm using Vpn pptp on the server setted up as provided from Randall Perry (
http://domain-logic.com/support/secure_tunnel.htm). 
The router configuration is: 
Precedence Interface Direction Src IP Addr/Netmask Dest IP Addr/Netmask Src Port Dest Port Protocol Tcp Flags FW Action 
10000 atm1 Any 0.0.0.0/32 0.0.0.0/32 0 80 TCP None Allow 
30001 atm1 In 0.0.0.0/32 external public ip/32 0 0 ICMP None Allow 
30000 eth1 In 192.168.1.0/24 0.0.0.0/32 0 0 ANY None Allow 
29000 Any Any 0.0.0.0/32 0.0.0.0/32 0 67 UDP None Allow 
29000 Any Any 0.0.0.0/32 0.0.0.0/32 520 520 UDP None Allow 
5000 atm1 Any 0.0.0.0/32 0.0.0.0/32 0 1723 TCP None Allow 
5000 atm1 Any 0.0.0.0/32 0.0.0.0/32 0 0 GRE None Allow 
5000 entries are related to VPN port. 
Also I configured a NAT policy in order to connect external public ip to SME server on 192.168.1.2.
...
thanks in advance