actually...
Frustrating, isn't it?
Actually, the fix is not *quite* as simple as noted above, because it's a default action that's dependent on an event, not a file type. Just had to figure this out the hard way - what you have to do is this:
1) connect the iPhone to your pc (close Word, and stop iTunes sync)
2) Control Panel (classic view)> Scanners and Cameras
3) Your iPhone should appear here as a camera. Right click and select "Properties"
4) Click the "Events" tab, make sure the "Select an event" pulldown is set to "camera connected"
5) In the "Actions" box, select "Take No Action" and hit OK.
That should do it!