the android version of the Acer Iconia 500 is either Honeycomb or ICS if the upgrade was done. You should see it as a media player when you plug it into your computer. You just need to drag and drop the file into the right folder on your Iconia (I don't use the Kindle app, but NoName has pointed out the right folder).
In Calibre, use the "Save to Disc" command and point it to the correct folder on your 500.
You can also save the book to a USB thumb drive, plug that into your Iconia and use a file manager (like
ES File Explorer ) to copy the book to the correct folder. (Just remember to unmount the USB drive before taking it out of your Iconia)