<p>I want (barely computer literate) people to easily submit a large number of files (pictures) through my web application. Is there a simple, robust, free/cheap, widely used, standard tool/component (Flash or .NET - sorry no java runtime on the browser) that allows a web user to select a folder or a bunch of files on their computer and upload them? </p>

swfupload
, the best tool I know that lets you do that. Simple, easy to use and even has a fallback mechanism for the  1% web users that don't have flash 8+.