access to web server through ubuntu server

Here is the configuration :
Internet---ADSL_router1---NIC1---Ubuntu_server---NIC2---ADSL_router2---Web_server

Ubuntu server :
7.10
Apache2
SSH

NIC1 -> $FW
opened ports are 80(http) 443(https) and 22(SSH)

$FW -> NIC1
everything is allowed

$FW -> NIC2
opened ports are 80(http) and 443(https)

NIC2 -> $FW
opened ports are 80(http) and 443(https)

Basically :
Ubuntu_server can connect to Web_server via NIC2 using Lynx.
From the Internet, Ubuntu_server is accessible via SSH.
Web_server only accept connections from Ubuntu_server.

What should I try to setup to allow someone from Internet to be able to browse Web_server (using a real browser like FF and not only Lynx) ?
The connection to Web_server has to be identified as being Ubuntu_server...

I'm admin of everything except Web_server.

I don't think this is hacking relative at all, but in case my opinion is false please feel free to tell it me.

Thanks in advance for any track you could give me.

Do you have forwarding turned on?

Code:

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echo "1" > /proc/sys/net/ipv4/ip_forward

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Hi Lazydog,
Thanks for your answer.
Actually there is no forwarding at all.
I know I can use that but the 'hard' part (for me) is that the request to Web_server seem to be originated from Ubuntu_server.
Unfortunaly Ubuntu_server has been turned off for the week-end so I can't send the ip_forward state (but it is at "0" right now).