Just tried booting Android using the guide on page 30.
Unfortunately, the kernel panic'd so I popped out the battery because I wanted to re-format the sd card and try again.
Now I'm stuck at a Nokia Screen with some icon beneath it (it shows a computer screen with a wrench above it)
When I pop out the battery and put it in again the device doesn't even try to boot, it instantly gets to that screen.

Any suggestions?

Edit: My computer recognises the N900 as an unknown USB Device in this state.
Edit2: Ok, managed to get it into flashing mode. Was quite tricky though: Had to pull out the usb cable, then pop the battery out. After that, I had to plug in the USB cable again and press U while putting the battery back in