The demos are not available to download (as a zip file, for example) but you can certainly check out the configuration options used in a particular gallery by viewing its 'config.xml' file directly in your browser. (You can check the path of the configuration file in the gallery's embedding code. If the gallery's embedding code does not set a configUrl, the the 'config.xml' file will be in the same directory as the HTML page displaying the gallery.)

Most of the demo galleries are available as presets in JuiceboxBuilder-Pro (the standlone desktop application to create and edit galleries which comes with Juicebox-Pro).
You can select a preset via the 'Load Preset...' drop-down menu on the 'Customize' tab.
If you want to inspect the preset files, you can find them in the 'Documents/JuiceboxBuilder-Pro/presets' folder (and you can open the XML files in a plain text editor to see the configuration options used).

Unfortunately, the Juicebox Plugin for Lightroom does not support presets in the same way that JuiceboxBuilder-Pro does.
To replicate a demo gallery, you'll first need to set the individual configuration options used in the gallery via the plugin's interface.
However, once you've got a gallery configured that way you'd like it to be, you can save the settings as a Lightroom template by clicking the + sign to the right of the text 'Template Browser' (in the left panel of the 'Web' section) and select a name for your template.
At any time in the future, if you want to apply these settings to a gallery, expand the 'Template Browser' control panel, scroll down to the 'User Templates' section and select your template.

I hope this helps.

Unfortunately, you cannot use a gallery's 'config.xml' file or a preset XML file in Lightroom.
You'll need to take a look at the configuration options (from a gallery's 'config.xml' file or a preset XML file) and then set these options individually and manually in the Lightroom interface. You can then save this combination of options in Lightroom as a template (which you can apply to future galleries).

The installation file for JuiceboxBuilder-Pro ('JuiceboxBuilder-Pro.air') is inside the Juicebox-Pro zip file ('juicebox_pro_1.5.1.zip').
Instructions for installing JuiceboxBuilder-Pro can be found here.

I'm not sure what you mean by "the dan created preset". Please let me know which demo gallery or preset you are referring to and I will point you in the direction of the gallery's configuration options so that you can set them in your Lightroom gallery.
Thank you.

The Juicebox Plugin for Lightroom does not support presets but there are individual controls in the interface for all configuration options so you can still replicate any gallery you like (with just a little more work than selecting a preset).

You can certainly process your images in Lightroom and then feed them to JuiceboxBuilder-Pro.
If you do not want JuiceboxBuilder-Pro to further process (resize) the images, then just deselect the 'Resize Images' checkbox on the 'Images' tab and JuiceboxBuilder-Pro will simply copy the source images across to the gallery's 'images' folder.

JuiceboxBuilder-Pro does not have any built-in FTP functionality but you can upload a gallery created with JuiceboxBuilder-Pro via FTP using a dedicated FTP program such as Filezilla.