It should be easy. First, plug in the Eris to your Mac using a USB cable (the one that came with the Eris is just fine.) It should put a notification on the Eris asking if you want to mount the SD card to the computer - go ahead and accept that. Since the SD card has photos on it, it may launch iPhoto automatically, asking to import your photos. If not, just start iPhoto manually and you will see, on the left, the SD card storage from your Eris, called "NO NAME" most likely.
When you are done, just remember to go into the Finder on the Mac and eject the disk called "NO NAME" before you disconnect the phone. You will also need to pull down the notification bar on the Eris after ejecting the disk to tell it to turn off disk storage. After you do that, you can disconnect the cable.
Also, while the Eris is connected and before you eject the disk, you can launch an application in your Application folder called "Image Capture". That will list the "NO NAME" disk in the "Devices" section on the upper-left. If you want it to always launch iPhoto whenever you connect, you can select "NO NAME" and, on the bottom left of that window, change "Connecting this camera opens:" to "iPhoto" from the drop-down control.