(I don't know enough about what I am trying to do to know if I am using
the right words in my question.  This is basic stuff for you
professional network admins.)

We have a new server that will take over the services from an old
server.  The data will be copied from the old to the new so that the new
can serve it.  However, we have a significant amount of documentation,
etc. that records document URLs from the old server.  We want the new
server to keep it's own, new hostname.  How do we slip the new server in
to take the URL requests of the old server?

Scenario:
(Names have been changed to protect the innocent, assuming there are any.)

Old server hostname: duck
Old server IP address: 192.168.1.3
New server hostname: eagle
New server IP address: 192.168.1.9

Old document URL (via http): duck/some/important/document.html
New document actual URL (via http): eagle/some/important/document.html

After the new server is in place any user or link that requests the old
URL, "duck/..." needs to be automatically redirected to "eagle/..."
What do we change to accomplish this?

Alan