Transparent proxy single machine question

[ken scott <kscott9@triad.rr.com>]

I am trying to build a single machine that  performs web filtering
(using DansGuardian)  for several users.
The box (Morphix/Debian system) will be behind a cable router and has
five users (kids).
I have running Dansguardian and Squid correctly in normal proxy mode.
The next step is to make the proxy transparent
so that users cannot bypass the Danguardian/squid path simply by telling
their browser to connect directly.
I have looked around and see instructions on this at several places
(mostly for non-single machine implementations)
and know I need a line something like like:

iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-ports 8181

       where 8181 is where Dansguardian is listening.

I also need to configure squid with (I think) :

http_port 3128     # where squid is listening
httpd_accel_host virtual
httpd_accel_port 80
httpd_accel_with_proxy  on
httpd_accel_uses_host_header on
httpd_accel_single_host off

The question is, on a single machine, will this work?
The part I can't figure out pertains to when squid finally wants to send 
out the actual
request to the internet, isn't that a port 80 request that the above 
iptables rule will
redirect back to Dansguardian??
Please reply all as I am not quite sure than I have joined the list 
correctly.
Thanks in advance
Ken S.