Here I will tell you as well:
1. Plug your USB cable into your computer and SideKick3
2. On the cccxcc,xzcxz,cbrowse to the SideKick3 drive folders
a)My way is to select and open "My Computer" then select the SideKick3
3. You will see two folders listed, make a new folder here, name it "themes" (without the quotes)
4. Open that "Themes" folder.
5. In that folder make another new folder with your new theme name.
a) This is the name you want to appear on the SideKick3 Backgrounds menu.
6. Open Windows Notepad and paste the following text into it
string Name(en_US) themename
bitmap ring-background ring-background.png
bitmap ring-folder-background ring-folder-background.png
7. Save this .txt file to your newly named folder as "theme.txt"
a) There are more strings that can be added and modified, this is a simple start.
8. Save the picture you want as the main background in this folder. (ring-background)
a) The name of the file should match the Notepad text file string.
b) Make sure its a .pgn or .jpg file, the text file should reflect the choice of the picture file format.
c)Sizing for backgrounds is commonly listed as 240x138 or 240x160 pixels
9. Add the second picture you want for the sub category background. (ring-folder-background)
a) This is the same size as the main background file.
10. The picture file names must match the text file to work, I sometimes save a .jpg image but still leave the .png in the text line and the background will not load.
11. Close the files, unplug your USB cable from the device.
12 . On your SideKick select Menu/Settings/Backgrounds and your new theme name should be listed below the original four. This is the name you set as the folder and in the text file.
a) Select the new theme and it applies.
Or, in easier terms,
hook your Sidekick up to your USB cord. Goto "My computer" and look for it to pop up and right click and click on "new" then "folder". Name it "theme".
Then double click on that folder and goto a site such as http://www.sk3themes.com/ and download a theme that you like. When it downloads it will download in a zip format, open it, and drag the folder with the
the title of the theme to your new folder. Disconnect your USB cord and goto your settings, and backgrounds, then you should see your new theme.