The "safely remove hardware" is something you should use, it doesn't uninstall anything, it simply checks and if neccessary stops any read/write cycles to the card allowing it to be removed. Removing any USB device like a card when it is actually being written to is asking for trouble.
Does Vista's "auto play" detect the card when you insert it. You say it's worked for 5 years ? What has ? Vista hasn't been around that long, do you mean your Nikon software... that's a diferent issue.
Have you tried another card, or reformatted this one and tried again.