USB Adapter Drivers

FTDI USB Virtual Com Port drivers can be downloaded from the list at the bottom of the page.

Windows XP, Vista, 7, 8 (32 & 64 Bit) - Win_CDM v2.12.00 WHQL Certified.zip. Download, unzip, and then run the self-installing executable file. You can also click on "View" and then download the executable file directly from the next screen with the download button on the right.
Max OS X - MacOSX_FTDIUSBSerialDriver_v2_2_18.dmg and see MaxOSX_TN_105 Adding Support for New FTDI Devices to Mac Driver.pdf for installation instructions
Linux - LINUX_ftdi_sio.tar.gz and see LINUX_TN_101_Customising_FTDI_VID_PID_In_Linux(FT_000081).pdf for installation instructions

These drivers are also available from the FTDI web site at http://www.ftdichip.com/Drivers/VCP.htm.

Les Kerr has tested the loading of the drivers onto various platforms. Here are the results of his tests:

Windows 8.1 (64 Bit) - "The first time I tried it, I got a mysterious "operation requires elevation" error. This was solved by running the installer in "program compatibility" mode. I uninstalled the driver and reinstalled it from scratch. This time it installed without complaining. I don't know why."

Windows 7 (64 Bit) – Absolutely no problem with the driver installation. Couldn't have been easier.
Windows XP (32 Bit) – For some reason it balked the first couple of times I tried it. Then it worked. I don't know what the problem was, but it was complaining that the program didn't pass the "Windows logo compatibility" test. I was trying to tell it to install anyway, and finally it did.
Linux (64 Bit) – The FTDI driver comes preinstalled with Ubuntu and Debian, which makes things a lot easier. It came up as /dev/ttyUSB0 on my Ubuntu system. The only complication is that I had to change its file permissions with the following command:

sudo chmod 666 /dev/ttyUSB0