Topic: I can't access all services by the router :(

[Napo Orso Capo]

I have this type of lan:
- a ADSL router with static internet IP
- a SME 5.0 server
- some Windows Client

All the systems are connected to a only hub.

The ADSL router (Zyxel Prestige) has the internal IP
192.168.1.1 and a internet IP.
The SME Server has the internal IP: 192.168.1.2
The SME Server make the DHCP function for the
others Windows client (from 192.168.1.65 to 192.168.1.250)

On the router i have imposted the ipforwarding for the
port 80 to the SME Server (192.168.1.2) but ... not work

If i try to connect from a external machine to the web server
of SME, i obtain nothing

I have tried with tcpdump to understand if some packet
are coming from the router and, the aswer is good: i can
seen that some packets come to SME server but ... without
answer.
The packet for the destination ip are lost

How i can correct this problem?

PS: sorry for my very bad english ... i speak italian and a litte of
german