Xp, firewalls and 2 network cards

Ive got windows xp set up in a windows 2003 domain.
The XP is functioning as the computer proving internet access and firewall to all pcs on the network. Ive got Kerio firewall 5.10 installed on the Windows xp machine which has 2 nics, one to the local network and the other to the internet.

Ive got a VPN server as well as outlook web access server behind the firewall. Ive mapped the ports corectly on the firewall (XP), that im sure!!

The problem is that all pcs have internet but any incomming traffic is not mapped to the servers, in fact it stops at the nic connected to the internet.
I need to be able to allow all incoming traffic on the windows xp (internet nic), to be allowed to pass through so that the firewall can take over, but no traffic is getting through the internet nic.
I have verified that iprouting in the regestry is set to 1, so that solution does not work.
Ive also tried enabling icf on the internet nic and mapping the port through xp, and still nothing. i need to open all traffic on the xp nics. Ive checked that there are no filters enabled, etc.

Please help