How do I prevent Dropbox from trying to import my scans?

Don't use Dropbox's Camera Upload feature with Doxie. Use the Doxie software instead.

On Mac OS X: https://www.dropbox.com/help/307/en
On Windows: http://www.groovypost.com/howto/disable-dropbox-automatic-camera-upload/

If you want to put your scans on Dropbox, save them to Dropbox after processing them with the Doxie app.