How can I get Windows 7 to recognize an external USB hard drive formatted by Vista?

"I had this same problem between a Laptop with Windows 7 RC and Desktop with Windows 7 RTM. It ended up being that the external drive was underpowered by the USB port on the Desktop. The solution was to use a USB Power Booster cable. The booster cable allows the USB device to draw power from 2 USB ports at the same time.

The reason some USB ports are underpowered for a lot of external usb hard drives is the fact that most of the drives use more power than the USB Specification states the USB port should support. The reason they work on some computers (I think most newer computers) is because the manufacturers go above and beyond the USB Spec for power output."