Proxying traffic across DMZ using IIS?

My employers are hoping to make material on an internally hosted
(private class IP) IIS server available to the internet. The machine
is hosted on a 3 network router/firewall: private, public and DMZ. I'm
interested in setting up some sort of proxying solution so that users
on the public network can download files from the IIS server on the
private network by connecting to a publically available server on the
DMZ. ISA is a bit overkill, I'm not looking for a total firewall
solution. Is there any way to configure IIS to pass incoming traffic
to another IIS server, and to pass traffic from that server back to the
requesting client?