Look in your control panel. There should be a way for you to determine what the automatic action should be whenever your iPhone is plugged into the computer.
I never tell Windows to do anything automatically when I plug in my phone/camera/ipod or even when I put a DVD in the ROM drive. Instead, it always just shows me a list of options as to what I can do. You might want to do the same.
if you go to Control Panel>Scanners and Cameras you should see your iPhone. Right click and select Properties. A dialog box will open up. Select the Event tab and you should see options to control what happens when you plug in your iPhone.