I recently bout Arduino Starter Kit that comes with Arduino Duemilanove ATmega328 and a bunch of LEDs, buttons, resisters and wires. I then downloaded the Arduino software from http://www.arduino.cc/en/Main/Software. I downloaded the Mac OS X version and installed it on my Mac Pro laptop. Once the software was installed, I launched the software and connected USB cable to the Arduino board as below:
Arudino software comes with a number of small applications and I tried their blink application by selecting File->Examples->Digital->Blink from the top menu. I then selected my board by selecting Tools->Board->ATmega328. Then I tried to look for USB connection under Tools->Serial Board, but didn’t see any. I googled for Arduino with Mac OS, and found USB driver, it required reboot so after reboot I was able to see it, e.g.
I inserted the LED to pin 13 that has builtin resistor, where the longer leg with positive charge went into the hole 13 and short leg went into the ground hole next to it. I then used the software to upload the application to the Arduino, e.g.
Voila, I was able to see the LED blinking, success.