[ale] I'm an iptables idiot

[Michael D. Hirsch]

What am I doing wrong?  I'm trying to forward port 2402 on one system to 
port 2401 on another.  This should be easy.

According to google, the solutions is the obviosu one, something like:
iptables -A PREROUTING -t nat -p tcp  --dport 2402 -j DNAT --to  \
           10.0.25.52:2401

In my searching I came across a bunch of folks who tried the obvious 
solution, it didn't work, so they asked the same question I'm asking.  
The responses were all variations on "You should try the obvious 
solution."

I believe forwarding is turned on:
# cat /proc/sys/net/ipv4/ip_forward
1

Suggestions?  I've gotta believe I'm missing something stupid.

Thanks,

Michael