The HMI430/700 is a USB composite device meaning it supplies more than one interface on a single USB cable. In the case of the HMI, it provides these 2 interfaces:
To allow the HMI430 to work on Windows Vista / 7 / 8.x, download and install this driver:
Be aware Microsoft Windows Vista / 7 / 8.x will all enumerate the file system without any driver. Simply connect the HMI430 and it will appear in Windows Explorer. However the serial port will not appear unless the driver file is installed.
The driver files have been signed with "SPLat Controls" so will install on Windows 7 / 8.x.
Windows XP does not correctly support composite devices so sadly the HMI430/700 will not work with this operating system.