To set up your magento 1.7 to allow the update of Min/Max Sale Quantities as well as Multiples through the api. Simply drop the app folder into your magento base directory. No magento core files have been modified so you are free to upgrade magento whenever.
This code has only been tested on Magento 1.7, feel free to branch/comment. Initially this was written to solve this - http://magento.stackexchange.com/questions/70804/update-minimum-sale-quantity-using-the-api