Pontus Frönder has put together a really simple USB interface for any LCD that uses the HD44780 controller. He used a USB chip from FTDI that creates a virtual COM port on the host computer. This is connected to an Atmel ATtiny2313 which controls the LCD. The AVR has two PWM outputs that are used to control the backlight and contrast. If the current draw of the backlight is low enough it can be driven directly from the USB and since it looks like a standard serial display you can talk to it using programs like LCD Smartie.