You'll need to format the SD card to FAT-32. To do so you'll need to click on the "Apple SDXC Reader" in the left column of Disk Utility.
Click the "Erase" tab.
Choose a name for the card (I chose Wheezy). For the format, choose MS-DOS (FAT).
Click "Erase" when you're finished.
Using the df command we're going to determine the mount point.
In the output, under the Mounted on column look for the name of your SD card. I named my WHEEZY so I'm looking for /Volumes/WHEEZY.
Then take note of the filesystem name in the first column. Mine is /dev/disk2s1. This is actually the partition name, but what we're really concerned with is the device name which is disk2. Copy this device name.
Hopefully by now the disk image is done downloading. By default, the disk image will download to your Downloads folder. Open up the Terminal application and type:
To locate the img type:
ls -lha | grep wheezy
You should see some output like this:
Downloads > ls -lha | grep wheezy -rw-r--r--@ 1 josephtyler staff 990M Feb 2 14:59 2015-05-05-raspbian-wheezy.zip
Now unzip the image. Make sure to use the name of your file.
Go back to Terminal (ensuring you are in the same directory as before), and type:
sudo dd bs=1m if=DISK_IMAGE_NAME of=DEVICE_NAME
Make sure to replace the values for DISK_IMAGE_NAME and DEVICE_NAME. Mine looks like this:
sudo dd bs=1m if=2015-05-05-raspbian-wheezy.img of=/dev/rdisk2
Enter your password, wait until it finishes, and you're done.
In the Win32 Disk Imager, click the blue folder icon and locate the Wheezy image you downloaded. Then in the Device box make sure the drive letter for your SD card is selected.
Click the Write button to begin.