383L+ images need 21 or 22 seconds to download in the best case. I would say that "Plan B" is working as expected on the 4 years old Windows XP deskop computer.
Do you have any other USB device connected to the new Windows 7 computer that would share the same USB host ? Try other USB connectors and try to avoid face connectors ... (i mean plug the 383 on a connector right on the motherboard).
JFYI, it's not a Windows 7 64 problem, i use two laptop with it and the 383, no problem.