so I started pulling my 770 apart. First I flashed in the developer rootfs, which turned out to be very striped down - so I decided to immediately switch back to standard and add a few things on the way. But first I needed to get the original image back, to do this you have to go here. And by the way, this nice awesome hardware is made in good old Germany!
I started going through the filesystem, a modified stuff like /etc/sudoers to include user ALL = NOPASSWD: /bin/sh so I can just get a root shell, without calling gainroot.
Searching further I found all the images, like the big Nokia logo that you see on startup (/usr/share/icons/hicolor/scalable/hildon/qgn_indi_startup_nokia_logo.png) and the Nokia hands (/usr/share/icons/hicolor/scalable/hildon/qgn_indi_nokia_hands.png). Guess what, of course I replaced them - no big magic. I also found this funny logo - actually its not funny if you get to see it (/usr/share/icons/hicolor/scalable/hildon/qgn_indi_startup_failed.png).
Also all the themes are nicely split up into multiple files, so modifying or creating new themes should be easy (I can't do graphics).
I guess I'll built me a real nice image over the next days. Also I don't know how the licensing is - can modified images based on the original firmware be redistributed?