I tried this a few weeks ago ('07 159) and thought I'd turned my stereo into a useless brick! Managed to get it all sorted though and I'm very happy with the results now...
I got stuck on what button combo to press and when, which left the install disk stuck on an loop where it only gets halfway and crashes.
I finally found this picture which really helped clear everything up. You have to press buttons 3,4,5,6 and 9 in quick succession before the install disk boots.
Then all of the lights flash and the system will reboot. Once this happens the installation should complete.
Hope this helps!
EDIT: Can everyone see the attachments? They're showing up in the preview but not the thread for me! (1st post sorry!)