Well, I did figure out the conflict, and it does not make the task any easier. My sketches are in a folder named 'Arduino Projects'. I recently installed Arduino 1.0.1 to try to catch up with the rest of the world. Since the new version did not directly support my processor (Mega644) I searched for someone who had modified version 1.0.1 and found one. They asked me to put their files in a folder named 'hardware' inside of my sketches folder. That seemed to work great for version 1.0.1, but ...All of the versions previously installed use the same skatches folder, and they also looked at that new 'hardware' folder and tried to interpret the stuff in it. When they could not, they spit out errors upon errors. So, I have to remove the new 'hardware' folder to use the older versions. Here is a partial listing of the errors I get when running Arduino_0021 with the version 101 'hardware' folder. The line in bold is the clue here.E:\Arduino Projects\Arduino\arduino-0021\arduino-0021\hardware\tools\avr\bin\avr-g++ -c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega644p -DF_CPU=8000000L -DARDUINO=21 -IE:\Arduino Projects\hardware\mighty-1284p\cores\arduino -IE:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial -IE:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial\utility E:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial\SoftwareSerial.cpp -oC:\Users\James\AppData\Local\Temp\build4082915697125474477.tmp\SoftwareSerial\SoftwareSerial.cpp.o E:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial\SoftwareSerial.cpp:24:24: error: WConstants.h: No such file or directoryE:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial\SoftwareSerial.cpp: In member function 'void SoftwareSerial::begin(long int)':E:\Arduino Projects\Arduino\arduino-0021\arduino-0021\libraries\SoftwareSerial\SoftwareSerial.cpp:51: error: 'HIGH' was not declared in this scopeI suppose that the same problem will occur on the Mac platform. So, the suggestion stands, in a modified form. Instead of 'make the PC like the Mac' how about thisMake it possible to have multiple versions of Arduino without any cross linking or conflicts. Put all modifications to the installed version inside of the installed version folder and don't allow overrides like putting a 'hardware' folder in a common folder like the sketches folder.