OK. Something to try.
Save a copy of your current httpd.conf file, so you have a backup.
Leave your public virtual hosts (unless they're really hosted somewhere else)as they are in httpd.conf.
For the fictitious ones, try changing to something like this:
NameVirtualHost 127.0.0.1
<VirtualHost 127.0.0.1>
DocumentRoot "C:\My Sites\Site1"
ServerName site1.local
</VirtualHost>
<VirtualHost 127.0.0.1>
DocumentRoot "C:\My Sites\Site2"
ServerName site2.local
</VirtualHost>
You'll probably want to find your "hosts" (probably in /private/etc/ directory) file on the mac, and edit it.
add the following lines to the bottom:
127.0.0.1 site1.local
127.0.0.1 site2.local
(replace sitex.local with your fictitious sitename.)
Restart apache. SystemPreferences>Sharing>WebSharing, stop then start.
Here's where I got this.
Step 1, google
http://www.google.com/search?hl=en&q=testinglocal+virtualapache
Step 2, click
http://www.apptools.com/phptools/virtualhost.php
(it's Windoze-based, but the concept is Apache,