The current prolific drivers do not support the older BU-353 chipsets (as stated on their website). You can use the older prolific drivers, though, and they will work with Windows 8.
I have a copy of the older 1.5.0 version of the Prolific Pl2303 drivers here:
I've tested these with Win8 x64 and they seem to work well.
Windows Update will try to update the older driver to the new version. If this happens, you can use the rollback function in device manager to get back to the correct version. Supposedly, you can tell windows update to ignore that driver for future updates, but I haven't figured out how to do it yet.