How To Install iPhone Themes
You will have to add a theme manually, if it is not available through the installer.
Use the installer.app and install OpenSSH on your iPhone.
Then, install WinSCP (File Protocol) on your computer. To connect to WinSCP you will need to go into your settings on your iPhone into Wi-fi, click on the little arrow next to the Wi-Fi you are connected to and get the IP address.
Now open WinSCP and enter the following values:
Your iPhones IP address
alpine and just hit login.
Then you'll want to answer Yes/Accept for the key prompt.
Create a folder with a title of your theme and a sub folder named "icons" that holds the required icon images.
Then, drag the complete folder into Themes on WinSCP and hit Copy.
Once it is transferred, you can go on your iPhone into SummerBoard and select the theme you have just added.
Just exit the app and the springboard will restart, and voila, your new theme will be up!