When you download and open .theme file you will be presented with a popup window ‘Subscribe to RSS Feed’ and you should click ‘Download Attachments’ so that each photo will be stored locally to be used as the wallpaper.
Each .theme file is the same, just with a different DisplayName and RSS feed source for the wallpaper.
Here is the base source code for each .theme file based on the Windows 7 Themes spec at MSDN as is a standard text file with a .theme file extension rather than .txt
*** Start Code ***
; Created by Stephen Edgar - stephen@netweb.com.au http://twitter.com/stephenedgar
; All trademarks and copyright belongs to the respective owners Microsoft, AFP & Dave Winer
; Any of my contributing code is licensed under a Creative Commons Australia license BY-NC-SA