Windows server 2003 proxy ARP?

Proxy are doesn't seem to be working on my Windows 2003
server. I am using it as a firewall and it needs to
respond to arp queries from the adjacent router on the
external network. THe firewall is setup to NAT private
addresses to public ( same subnet as the router )
addresses. The firewall is configered to respond to ARP's
for those addresses for which it is NATing. For return
packets the router ARP's for the MAC for the public
address that had previously been translated. The server
should respond with its external ethernet MAC address.

I removed the firewall software and Windows still does not
respond to the arp's even though I made permanent entries
in the arp table ( arp -s ). Any suggestions?