These are for windows 8.1
for separate x86 and x64 driver you can use
http://www.ftdichip.com/Drivers/VCP.htm
you need to install them manually from device manger. first for the FTsomething unknown device and then for the Virtual com port both drivers are in the same folder.
I used this method and it worked for me.
Another method is to get the setup to do this for you.
for a driver setup use
http://www.ftdichip.com/Drivers/CDM/CDM%20v2.08.30%20WHQL%20Certified%20for%20Windows%208.1.exe