The content of this post is largely taken from http://currentcost.posterous.com/windows-7-data-cable-drivers, the Current Cost blog.
To connect a Current Cost ENVI to Google PowerMeter, you have two options – either purchase a Bridge from SmartNow http://www.smartnow.com.au/current_cost_bridge.html or you can connect through your PC using the optional USB cable. For most versions of Windows and Mac you need to install the Prolific driver.
However, it is not necessary to install the drivers for the Data Cable for Windows 7. Simply connect the Data Cable and the drivers should be located and installed automatically. If you have previously installed the Data Cable drivers and cannot get the Data Cable working correctly, please follow the instructions for “Uninstalling the Data Cable Drivers”. Uninstalling the Data Cable Drivers With the Data Cable plugged in to the PC, go to Control Panel -> Device Manager. Expand the Ports node. Select the “Prolific USB-to-Serial Comm Port”. Right click – uninstall. Click to view large Download this gallery (ZIP, undefined KB) Download full size (146 KB) When the uninstall is complete, unplug the Data Cable from the PC. Go back to Control Panel -> Programs and Features. Select the item called “PL-2303 USB-to-Serial” and click “Uninstall” Follow the wizard to complete the uninstall process. Reboot the computer.