To install the WinUSB drivers for the LPC18xx/43xx boards, first configure the board for USB boot. Plug in the USB connector to the board (add external power to the board if necessary) and a new USB device (LPC) should appear.
Download the drivers at http://www.lpcware.com/content/nxpfile/lpc18xx43xx-winusb-drivers-dfu-boot
Un-compress the drivers and point the driver installation dialog to the INF file in the uncompressed package. You may get a security alert that Widnows can't verify the driver's publiser. Select the "Install drivers anyway" option.
After installation is complete, you should have a new device available for the LPC18xx or LPC43x.