[UPDATED on September 19, 2010] 海外フォーラムによるアップデータを利用したKindle3のハックが可能になったようです。興味のある方はグーグルで検索してみてください。
English version This is a /NOT/ easy hack such an update_*.bin on kindle2/DX. And you /MUST/ have serial line connections. AT YOUR OWN RISK.
1) Prepare for pictures. GIF or JPG, W600xH800. File name is anything ok. Kindle automatically sorts by numerical-alphabetical order. 2) Connect Kindle and PC via USB and copy these pictures to Kindle USB storage 3) Disconnect USB 4) Establish serial line connections with Kindle and PC (minicom, TeraTerm, etc) 5) Backup original pictures of /opt/amazon/screen_saver/600x800/* 6) Copy your pictures to above directory 7) Reboot
Confirmed this works under Kindle Software 3.0.1
If you have a skill enough to make serial line connections, this is very easy. But, for average users, making serial line is very very tough and dangerous work. Therefore I strongly recommend that you wait for easy hack to be released from skilled hackers, before you step forward to the point of no return.
[UPDATED on September 19, 2010] As I said, great skilled hacker released easy hack way. If you have any interests in this matter, please do Google search.