[CentOS] iptables nat PREROUTING chain

Is there a way to add a rule to the nat table (CentOS 5.7) that would alter the port number of tcp packets destined for the server itself? I have ip_forwarding enabled, but the packets don't seem to hit the prerouting chain.

I have the following redirect rule in the prerouting table. I also tried DNAT, but if the packets don't hit PREROUTING, it won't work either.

iptables -t nat -L -v -n Chain PREROUTING (policy ACCEPT 16079 packets, 896K bytes) pkts bytes target prot opt in out source destination 0 0 REDIRECT tcp -- * * 10.10.10.0/24 0.0.0.0/0 tcp dpt:25 redir ports 12345

aspen 2# cat /proc/sys/net/ipv4/ip_forward 1

Thanks, Nataraj