Uploading Marlin Firmware To Melzi-ATmega1284p
It looks like the Marlin firmware supports two versions of the Melzi board, although it isn't clear if it specifically includes the 2.0 version. The best thing to do is just try it. In the Configuration.h file find the section where it says:

#ifndef MOTHERBOARD
  #define MOTHERBOARD BOARD_ULTIMAKER
#endif


Now replace BOARD_ULTIMAKER with BOARD_MELZI_1284 and try that. If that doesn't work you can try just BOARD_MELZI. If neither of those work, you are out of luck, unless you are willing to dig in and do the pin mappings yourself.