What I meant was, what specific and ExpressCard/34 model, as there are quite some out there. Did it come with any drivers on a CD/DVD or does the official support website of that product offer any documentation or software?
Did you boot the MBP while the ExpressCard was already inserted?
Does the ExpressCard show up in System Profiler?
Does it show up in Disk Utility with an SD card inserted?
Do you have the Aluminium (1) or Unibody (2) MacBook Pro?
Actually, you can go to "Product & support" > "Driver Download" but even there nothing is listed for MAC.
Seems like you are out of luck, perhaps, unless someone here has actually can provide the driver having bought the same card years ago and if they ever had a driver. The website is from 2005 ..mmmhh, all other products support only older system, and this makes me wonder if even the actual driver would work under the current Snow Leopard OS.
Honestly, I don't want to offend you, but for me looks like just another case of someone unloading surplus stuff to people trying to save a buck. Wish you good luck but you might want to consider to check with some proven Mac-accessory suppliers.