In the general case, you should be able to extract the VID/PID and device class codes from the node in the device manager corresponding to the unknown device. Finding VID, PID, REV, CLASS, SUBCLASS, PROTOCOL etc. You can get driver packages for both easily on-line, and the odds that one is right are pretty good. Its not a general solution, but a USB to RS-232 interface cable has a high probability of being built out of either a Silicon Labs CP210x chip, or a close relative of the FTDI FT232R chip.
