Not too familiar with PC or the current status of 1.1.1 3rd party support but I have the Installer on my iPhone and have added additional Community Sources like HighTymes.
To access this source, go to this thread and on the second post, you'll find
HightTymes' post with a downloadable "Additional Installer Sources" and instructions on where to put this source file.
You'll then find these sources in Installer under "Themes (SummerBoard)".
These files, when installed, will show up on SummerBoard's pref Theme selection in your iPhone.
On the Mac, I just perform SSH to add some themes (that are not found on the Installer) where SummerBoard/Themes folder resides.
Good luck!
