I am not the original author, but I converted the program to maemo4 (diablo and chinook) so I think I can provide some insight.

When converting the desktop applet I left everything as the old maemo3 (bora) style declarations, rather than convert them to maemo4 declarations. This works fine for loading/unloading the applet, but you won't be able to do everything you can do with maemo4 applets. I am pretty sure you will have to convert to maemo4 style before you can implement transparency.

I wrote Personal Launcher (which uses maemo4 style declaration) and the transparency code for OMWeather, so those would be a good way to start changing the code for transparency.

I found that the API documentation for maemo4 desktop applets was better, but the maemo3 tutorial for writing desktop applets more helpful.

Maemo 3.x: How to write maemo desktop plugins for maemo
Maemo 4.0.x: Writing Hildon Dekstop Plug-ins for Maemo

Let me know if you have any specific questions, I may be able to help.

Andrew