You'll need a memory card.
(Delete the Themes folder you may have created on your Sidekick. We're starting from scratch here.)
Plug your Sidekick 2008 into your computer using the USB cable.
Create a new folder on your Sidekick 2008 named Themes. It should be in the same window with the DCIM and Music folders.
Download a theme from sk08Themes
and save it to your computer (NOT to your Sidekick)
Locate this file and right click on it and click Extract All..
You should be looking at the Extraction Wizard. Click Next
Click Browse and select the Themes folder on your Sidekick 2008.
Click Next and watch the progress meter go as the theme is placed on your Sidekick 2008.
When this is done, click Finish to exit the Extraction wizard.
Unplug your Sidekick 2008 and then select your new theme from the Backgrounds menu.
Repeat steps 3 through 8 for each theme.