tcp/ip port mapping and url path

Hi Everyone,
 
I've run into a situation with HTTP where I have 3 different HTTP web
instances running on an AS/400 v5r3, and before they go through our
firewall and hit the outside world, I need to bring them all together on
port 80 (default HTTP.)  To clarify, the url paths for all 3 are
different/unique as well.  
 
The other side of this is, when the requests come into our network on
port 80, I need to segregate the requests to their correct ports, before
the requests hit the web server on the 400. I have been looking at a
variety of ways to do this, including NAT on the 400, which seems to be
able to handle all of what I need EXCEPT the segregating by url path.  I
am curious if there are Exit Point Programs available, that may do this
last piece for me.
 
The other question is, if I turn NAT on, will it only affect what I
specify, or will it affect all TCP/IP activity on that machine?
 
I'd really appreciate any advice, comments, etc. you can share with me
on this. 
 
Thank you,
Jeff



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