Ok, here is my first attempt to produce a working theme... It's inspire by iTunes on Mac OS X.
It's almost complete, but I've one bug with the PAL BM configuration : the position of texts is not the one I defined on the PBAT script after a cold start of the PS2. I have to switch to default theme and come back to my theme to make it work.
I don't have this issue with NTSC or 480p BM display.
Also, I could not test the VGA mode as I don't have a VGA cable...
I hope you'll enjoy it and that it will give you the will to make and to share your own.
And if you manage to make a more than 400x240 image, please let us know.
ITUNES.zip