I'd like to have Apache 2 listen on both loopback (127.0.0.1) and eth0
(x.x.x.x). If a user connects to loopback, he gets the site. If he
connects to eth0, he is required to enter a password first. How can I
do this?

(PS Also, how could I make the site on eth0 different?)

Using Apache 2 on RHEL 4