This uses a modded version of the tga injector, but you don't have to use tga's.
To create a transparent wave, is not easy. If you want to try a tga make sure is it in grey scale mode. DO NOT use :Photoshop, only gimp will work. The wave show above is a PNG, renamed. I have also use 17kb of "FF" data, and gotten some nice a wave.
The trick to the hole thing is, that the wave will not look, or act the same on any other themes. Keep playing with data until you get something that works with your theme.
I'm not sure, how else to help.
In short, save some data as a tga, and make sure the file is not over 17kb.