The biggest issue on a starting point is unlocking that storage card so you can get to it in other devices. I can understand why you didn't post the password, but that remains the key....
Getting root is easy once the card is unlocked -- mount it on another unix-style machine, stuff "su" in the /system directory and flag it SUID, then stick it back in the head unit!
That also leads to another interesting thought -- if you stick a file manager in the system directory along with /bin/su, you should be able to navigate to an attached device (e.g. SD card in the front, attached USB disk,