I would rather suggest you to use the USBUART. It has the advantage for communicating in both directions with your PC using something simple as HyperTerminal on PC side.
I know the USBuart, I use it on another project, but I want to try with HID, because it's plug and play.
I would like to make an card like this:http://www.phidgets.com/products.php?category=0&product_id=1012_2
So what you want is to send commands from you computer to your MCU?
You can do that using an OUT endpoint. Use USB_EnableOutEP() to enable the out enpoint and when wGetEPCount() says there is some data, read the enpoint using USBFS_bReadOutEP()