netfilter PREROUTING question/problem

mod_mp3 list:

On a linux box's netfilter firewall I'm trying to route requests to an
apache mod_mp3 enabled machine behind the firewall.  The mod_mp3 instance
is working correctly with requests from machines within the firewall (i.e.
I can get play lists, play ogg files, etc.).  On the firewall I use the
netfilter PREROUTING chain to alter the incoming packets on port 8000 to
route to the mod_mp3 instance behind the firewall which is also listening
on port 8000.

Any request I send to the prerouting port on the firewall from the outside
never gets a response from the inside mod_mp3 instance.

To debug my netfilter commands to make sure I wasn't getting the
prerouting wrong I prerouted requests successfully to the inside apache's
port 80 as well as logged debug warnings to the LOG target on the firewall
itself.

Hopefully I'm just missing some netfilter commands and someone on the list
can send me some advice.

Thanks much,
Mike

p.s. I read through the lists archive before sending this note.