I use it on my Kindle 2 (international version).
Have both the "letter.bin" and the "uninstall.bin" on a safe directory on your computer.
Attach your DX via USB cable. Open your Kindle (mimmics as an USB mass storage) and copy the "letter.bin" to the root of it. Safely eject it and then go thought Menu> Settings >Menu >Update your Kindle.
Your Kindle will reboot and your new font will display. Should you reverse the process simply do the same process with the "uninstall.bin".
Hope that helps.If anyone could explain the process in a better English, please be my guest.