I didn't install the FTDI drivers for the usb-serial device as mine is a prolific. see pics below for what my device maanger is showing, this may not help, this my not be the same for your usb-to-serial device. There is a pic that shows the uk ebay item for the usb-to-serial i a m using. This was the second usb-to-serial device I bought as the first device (not this model and make) didn't work, so just in case be aware that only some of the devices are windows7 64bit compatible. this one was very cheap, 5 pounds.
hope that helps
karl