DNS resolves appropriately -- 

$ host myclient.ida.campaignfoundations.com
myclient.ida.campaignfoundations.com has address 204.232.201.213

My apache configuration passes a syntax check -- 

# apache2ctl -S
[Sat Feb 25 18:26:38 2012] [warn] NameVirtualHost *:80 has no VirtualHosts
VirtualHost configuration:
*:80                   is a NameVirtualHost

  .  .  .  


         port 80 namevhost this_vhost.myclient.org (/etc/apache2/sites-enabled/006-myclient.org:2)
         port 80 namevhost myclient.ida.campaignfoundations.com (/etc/apache2/sites-enabled/006-myclient.org:27)
         port 80 namevhost that_vhost.myclient.org (/etc/apache2/sites-enabled/006-myclient.org:52)

  .  .  .  

Syntax OK

The appropriate vhost shows me an expected DocRoot -- 

# less /etc/apache2/sites-enabled/006-myclient.org

<VirtualHost *:80>
        ServerAdmin hesco@yourmessagedelivered.com
        ServerName myclient.ida.campaignfoundations.com

        DocumentRoot /var/www/sites/myclient.org/drupal-6.22
        <Directory /var/www/sites/myclient.org/drupal-6.22/>
                Options Indexes FollowSymLinks MultiViews
                AllowOverride None
                Order allow,deny
                allow from all
                RewriteEngine on
                RewriteBase /
                RewriteCond %{REQUEST_FILENAME} !-f
                RewriteCond %{REQUEST_FILENAME} !-d
                RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]
        </Directory>

        # Possible values include: debug, info, notice, warn, error, crit, alert, emerg.
        LogLevel warn
        CustomLog /var/log/apache2/myclient-access.log combined
        ErrorLog /var/log/apache2/myclient-error.log

</VirtualHost>

The apache owner has permissions to read files in DocRoot -- 

# sudo -u www-data less /var/www/sites/myclient.org/drupal-6.22/index.php

again shows me expected output

My logs (error and access) include no clues with my IP and the expected date-time stamp.

And still my browser reports:

Forbidden
You don't have permission to access /index.php on this server.

This appears to be the logs:

[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.html denied
[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.cgi denied
[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.pl denied
[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.php denied
[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.xhtml denied
[Sat Feb 25 19:54:22 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /index.htm denied
[Sat Feb 25 19:54:23 2012] [error] [client 174.48.250.91] (13)Permission denied: access to /favicon.ico denied

But www-data ought to be able to read my 644 perm'd file -- 

-rw-r--r--  1 hesco hesco  923 2011-05-25 16:43 index.php

following the advice at: http://wiki.apache.org/httpd/13PermissionDenied 
namei output looks like this:

$ namei /var/www/sites/myclient.org/drupal-6.22/index.php
f: /var/www/sites/myclient.org/drupal-6.22/index.php
 d /
 d var
 d www
 d sites
 d myclient.org
 d drupal-6.22
 - index.php