I found a workaround for the prolific driver problem [note: this was with another prolific USB-Serial device showing the same problem, not a CurrentCost cable]
It's originally from this page : http://social.technet.microsoft.com/For ... 096b46131/ - look for the post by drtedrted half way down the page. He has repackaged the older prolific driver files into a little zip file (got rid of the installer).
Here's what to do...
Download the zip file from http://sendspace.com/file/5m5afw
Unpack it
Go to the unpacked files, right click on the ser2pl.inf file and choose 'Install' from the menu. You should get a success message after a few seconds.
Plug in your USB-Serial lead, wait for all the driver installing stuff to finish
Start up device manager - the Prolific USB Serial device will probably have a yellow error icon on it.
Right click on the device, choose 'Update Driver Software'
Choose 'Browse my computer for Driver software', then 'let me pick'
You should see a list with 2 versions of the driver. Choose the 3.3.2.102 version and press next.
Your USB serial device should now be working
I must say I'm not impressed with the attitude of Prolific here - it's seems very likely that they've deliberately bombed their drivers to stop these chips working on Windows 8. They haven't given a clear technical reason why Win7 should support these chips and Win8 shouldn't and they haven't gracefully withdrawn support but left the devices working. Not so long ago, Prolific was the USB-Serial converter of choice as the products tended to work well and have driver support in various OS - not so any more...
Robin