I am having trouble downloading a program onto the Arduino. How can I fix this?

Make sure you have the correct serial port selected. Goto Tools->Serial Port and select the right serial port.

It is quite possible that the Arduino software will spontaneously deselect the serial port you have set previously. It is also quite possible that the assigned serial port changes.

How do I know which is the right port?

(Windows) It's hard to tell, just try them all :)
(Mac) You guys might have a much longer list. I think there's something specific that you could be looking for, but I don't know which it is.

It still doesn't work. What else can I do?

Try unplugging the USB cable, shutting down and restarting your computer. Plug the Arduino back in BEFORE starting the software again.

I am running MacOS X and I can't get Processing to talk to the Arduino. How can I fix this?

1. Quit Arduino environment and Processing environment. UNPLUG THE ARDUINO BOARD FROM THE USB PORT. Don't skip this step, it's the most important part
2. Browse to /Processing 0125/libraries/serial/ Under this directory should be a file called "macosx_setup.command"
3. Double click this file, and go through the instructions
4. Restart Processing, Arduino, etc
5. Your port will probably be something like "/dev/tty.usbserial-4001nvG", it's listed in the Arduino program under the menu "Tools -> Serial Port". Make sure to put this into your Processing application, otherwise Processing won't know where to listen to the Arduino board.

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I am running Windows Vista, but having trouble with the Ardiuno. How can I get this to work?

There is an unstable version of Arduino for Vista. Give it a shot! (Link)

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