After searching for 'simple instructions' for the Picasa Plugin, I have decided to figure it out and share my findings with you.
YOUR WEBSERVER
Create a directory on your webserver where you will be placing your photo albums.
For example; photobook. The directory would be located here;
http://www.domain.com/photobook
PICASA
Using Picasa, export your pictures using the XML template.
This will create a directory on your computer that contains two subdirectories (named images and thumbnails) and a file called index.xml.
The name of the album you define in the process is what the directory will be called and later show up online. Choose wisely, however you can change it later on if you don't like it. In our example; I named the album 'vacation'.
YOUR WEBSERVER
Now FTP this entire directory into your photo albums directory on your server.
So, using our example, it should be located here,
http://www.domain.com/photobook/vacation
SERENDIPITY - PICASA PLUGIN
Install the Picasa plugin. This should be pretty straight forward.
Let's configure the plugin. We will get this working, then you can configure to your liking.
To start, choose 'Yes' for ENTRY_BODY, EXTENDED_BODY, HTML_NUGGET.
Path: This is the URL path to your album directory you defined above;
http://www.domain.com/photobook There is no trailing slash.
Show title of the albums: choose 'Yes'
Open the target window using JavaScript: choose 'Yes'
Smarty Template: choose 'Tnt Gallery' to begin.
Ok, now the plugin is configured.
SERENDIPITY - CONTENT
Let's show a gallery on the site.
Create a new entry and (using our example) type in the Entry Body the following; [photobook]vacation[/photobook]
The format is always: [your album directory]your album[/your album directory]
Save this entry.
You should now be able to view the images online.
Hope this helps.