I'm no expert, but I plugged in the cable & when the hard drive icon came up on my desktop, I moved it to IPhoto & the images appeared. I think you have to click on "import" to keep the photos in Iphoto. Fiddle around with it. If I can do it, you can too! You have to drag the hard drive icon into the trash before unplugging the cable.
I'm no mac user, but could you take the SD card out of the camera and plug it into a SD Reader attached via usb to your PC and then do like-wise with the drag and drop, copy paste of the photos you want on your PC?
Not sure if this will help, I use a Mac as well and I have both used the USB connector and placing the SD card directly in my Mac. Have you tried using a different USB port (if you are connecting the camera directly)?