I'm not sure what the trouble is that the original poster is having. As I mentioned before, I have noticed occasionally that nothing happens in the Finder when I pop in a SD card in, but Aperture will launch and can see the photos on the card. Lacking a copy of Aperture, iPhoto should automatically launch when a memory card from a camera is inserted, whether it's via an ExpressCard or an external USB card reader.
Have you tried rebooting the computer, with the card inserted and the reader plugged in?