Subdomain forwarding to other IP

[joximu]

Ah, am I understanding right?
Your Lan:
- a webserver "A" which is contactable from outside (Port 80 in the router directs to this server "A").
- another webserver "B" which is not reachable from outside.

You want webserver "A" to show the content of webserver "B" also to the outside?

If this is the case, I think you need mod_proxy - or another proxy software (you mentioned squid) - but mod_proxy may do this - see on the apache website for more infos and docu.
A redirect only gives the browser an information where to go next...

/J