The best way to read Manga on the Kindle 2 is to use the Mangle program from Foosoft. It is specifically designed to convert images for best readability. It's been working great for me.
The site:
http://foosoft.net/mangle/
Some other thoughts and images of content:
http://www.insomnicdreams.com/2009/0...es-for-kindle/
I have run into a problem with firmware 2.3 and the photoviewer that makes images a little harder to use. Hopefully the bug report I've filed will correct the issue. With the 2.3 firmware update adding PDF support, combined with the Mangle conversion it has still been very workable to read manga on the kindle.