I ran into a similar issue with Windows 7 64-bit and Arduino 1.0.3. I have an Uno R2 board and an Uno SMD R2 board and they work fine. My PC would not recognize the new Uno R3.
After a little diving in the arduino/reference/Guide_Troubleshooting.html document that comes with the IDE I found this:
On Windows 7 (particularly the 64-bit version), you might need to go into the Device Manager and update the drivers for the Uno or Mega 2560. Just right click on the device (the board should be connected to your computer), and point Windows at the appropriate .inf file again. The .inf is in the drivers/ directory of the Arduino software (not in the FTDI USB Drivers sub-directory of it).
In doing so, my Uno R3 is now recognized and working as expected.