http://www.enterpris...doc/devguide.html
all the customer needs to do (from your description) is non tech people need to easily upload a large file to you, so a browser based app would
ask what file the customer wishes to send including how to find it (attachement function generic)
click "yes this is the file I weant to send"
browser client needs to tell customer status of upload (activity bar) and a notification of when it is finished (pop box "we're done!")
now get a little fancier and provide a toolbar icon and make the whole thing a plugin.
does that help a little bit?