Link to the current version of the Digi RF Driver Installer for all versions of Windows:
For Linux and Macintosh OS X, it's highly recommended to download and install the drivers directly from FTDI. The download page is located here: http://www.ftdichip.com/Drivers/VCP.htm
Legacy XBIB-U / PKG-U USB Drivers for Windows 98 SE - XP
Legacy XBIB-U / PKG-U USB Drivers for Windows Vista and and Windows 7
Legacy XBIB-U / PKG-U USB Drivers for Linux
Legacy XBIB-U / PKG-U USB Drivers for MacIntosh OS X
For instructions on how to load these drivers manually in Windows Vista, and Windows 7, please refer to this document: How to Install USB Drivers in Windows Vista & Windows 7
If installing FTDI Chip drivers or legacy drivers, it will be beneficial to Optimize USB to Serial Port Settings in Windows to ensure proper operation of the radio.