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To use a theme what you would need to do is download the theme pkg so you have all of the images.    You would need to upload the images to your own image host then replace the image links throughout the css.    If the theme requires template edits it gets trickier because you cannot edit templates.   You would need to figure out how to use your header and possibly footer and the html to put there so you can get the same look.   Its not always possible to recreate a theme.   It was easier with smf 1.1.* to do that - with 2.0 its a whole nuther ballgame.
 
The poker one you are looking at -  I don't think it could be re-created and that's what you would need to do - themes cannot be installed.