Here's 4 MAX7219s controlling 256 LEDs controlled by an Uno or Duemilanove.
Controlling them from another source would be straightforward.
Send in simple message, like
xxx, 0 or xxx, 1, where xxx is the LED number, and 0 or 1 is off or on.
The controlling Arduino then maps xxx into MAX7219 1 to 5, and then into register 1 to 8 of each device.