Windows will match a driver as specifically as it can, so a vendor can bug-fix a product without using up one of their precious PID codes by modifying the revision code, and produce a driver that compensates for the bug in old devices by matching it to the triple of VID/PID/REV. The list linked by Dennis is kept reasonably up to date, and may be the quickest way to just look up a vendor name. The VID can usually be translated to an actual vendor name since vendors are supposed to buy VIDs and register with the USB-IF.
VID and PID can be read from the Details tab, by selecting Hardware Ids, and the Class and Subclass by selecting Compatible Ids. 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.
