I saw your post on the whirlpool forums and had tried to do the same thing your doing (fairly computer savvy) but I could not for the life of me get a working update.img. Tried again after reading your post and still failed. ADB wont let me push the file to data nor even though I have mounted it as read/write.
What I have done though is make a working dump file that you could then extract the update.img file from, As to how to do this I am stumped again but I have followed the steps listed Dump your Home Tablet rom and create a custom rom - Wiki.ArchosFans.com
I have the backup.Dump file which I will upload to mediafire soon, Maybe you will have better luck or maybe you can explain to me what I need to do (I believe its listed under Additional Info But do I need a hex editor and if so what am I looking for?).
Will edit post with link for Backup.dump soon.
And here it is http://www.mediafire.com/?qy73cgaaq11gb3a