You still having problems? I've got a very simple config (still working on complex config) that forwards port 80 to an internal machine and would likely work with any mainstream service you need to see from the outside. First line of *nat PREROUTING

iptables -t nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.1.10:80

and the kicker (b/c I am dropping Invalid & New connecitons)

iptables -A FORWARD -d 192.168.1.10 -i eth1 -p tcp -m tcp --dport 80 -j ACCEPT

Outbound traffic from 192.168.1.10 is NAT'd.

You might be working with a more complex setup but I thought I'd throw it out there.