I recently discovered how to read Kindle books on my Simple Touch, and thought I'd share the process here for those who might be interested. Let me clarify first and say that I have not rooted or altered my NST in any way.
1. First, if you haven't you need to install Kindle for PC on your computer; and also Calibre.
2. Open the Kindle program and download the book of your choice
3, Open Calibre and choose "Add book" Find the book under My documents, My Kindle content. It's going to have a weird name...most probably with a blue book icon next to it.
4. When the book has been added to Calibre, you will need to convert it to an epub. Just click convert at the top of the page; and let Calibre do it's work. (Now, if you come across a DRM issue...well, there are ways around that; but I'm not here to discuss that aspect of it. For the purposes of these instructions...try a different book)
5. Once the book has been converted, connect your NST with the USB cord to your PC and then choose the "Send to Device" option shown at the top of the page. Send it to the main memory; and Viola...your Kindle book is now on your NST for you to enjoy!
Perhaps many have already figured this out...it took me forever, though! So, I wanted to share it. I am a lover of all books both Kindle and Nook; but I only have Nook devices. I have a Nook HD plus which will allow me to read my Kindle books easily via the app; but I can't do that with my NST. I enjoy using my NST while travelling and outside reading, however and want to be able to enjoy all my books on there as well.
Anyhow...I hope this helps someone too!