I was playing around with it last night without any luck. I tried hooking it up similar to the instructions here - http://arduino.cc/en/Guide/ArduinoMini
. When I first plugged the USB board in, XP couldn't find a driver, so I downloaded one from the FTDI site and that seemed to keep it from complaining. I think it still wanted a drive for a USB Serial connection or something though, didn't figure out what it wanted though.
When the Arduino was powered, I got the constant red LED for power and the green LED on pin 13 started to blink. The pattern was like it was driven with PWM and the duty cycle kept increasing until the light appeared solid, then repeated. I tried hooking up the FTDI header at the top of the board instead of the pins on the side. I hooked up the power, gnd, TX, and RX pins, but that didn't work. I also tried hooking up DTR to 5V, then to ground, but that didn't do anything either. When I tried programming, I couldn't get anything to work, obviously. When I checked the serial ports, it only showed 2, but I have more USB ports than that. Neither worked for any configuration I tried, of course.
I just bit the bullet and ordered an FTDI breakout board from SFE, so hopefully it'll get here soon and I won't have to dick with it anymore. If you figure it out, I'd be curious how you did it. Know of anyone who needs a spare Arduino USB board?