I set up a localhost testing server following the tutorial. Using MAMP. All working fine. My question; I need to develop/test 3 seperate WP sites locally. Is it possible to set this up? I can't find any imediate info on how to achieve this.
If you followed the tutorial I think you did, then you installed WP in the root of the web server. Log into the wordpress installation and change the path to a subfolder (Settings->General). Then move all the Wordpress files into that subfolder. Then start up Wordpress again. And if you need to make anymore installations, install them in other subfolders so you end up with http://localhost/subfolder.
Consider DesktopServer Limited, it does what MAMP Pro does for FREE and even includes the latest version of WordPress. Also, you can copy your complete site, settings, plugins, themes, etc.. Great way to template and jump start your projects.
The Premium version goes beyond any other webserver by automatically creating Dreamweaver site definitions, supports LiveView on template files (not just index.php) for true WYSIWYG WordPress theme development.
I do what you are after using Wordpress Networks (I think it used to be called MU)
I have a local test server with a local wordpress installation and develop child themes using that set up. I link that my own development site and it all works ok for me. You have to do a little more jiggling about to set up a Wordpress Network but there's plenty of stuff in the wordpress.org site to help you with it.
Obviously, there's a bit of thinking to do and I don't add a lot of content. It does help with developing the site structure and the CSS though.