Ouch!
Same thing happened to my 8Gb a while a go, this worked for me, so it might or might not work for you. Vista was having problems opening the SD. So I decided to try to open the card in another OS (in this case I had an Ubuntu 8.04 Live CD lying around that I had never used). So I booted up Ubuntu, inserted the Sd in the PC and for some reason, Ubuntu was able to read the content of the SD when Vista couldn't. Don't know why, but if you're desperate, if could be worth giving it a shot.

Anyways, good luck and keep us posted!