http://bentasker.i2p/posts/documentation/development-programming/175-allowing-file-uploads-direct-from-dropbox.html
It makes life a lot easier for your users (especially those who want to upload from a *cough iOS* device with file uploads disabled ) and the hassle of setting it up is minimal. In this post, I'll be showing how to implement the Dropbox chooser into a simple PHP site So, let's start by creating a simple upload form, allowing the user to use either the standard upload element, or the Dropbox chooser.