Hmm. On my PC (Windows XP), when I plug the Story in a window comes up immediately for the SD card, and then that Windows selector dialogue asking what I want to do with the files on the new device comes up. (You know, do I want to play the music files, open an Explorer window to browse the device, yadda yadda.) It's only when I click on the option to open an Explorer window that a new window comes up with a drive letter allocation, showing me the files on the Story itself.
So, am I correct in assuming this latter step - letting you browse the device - isn't coming up?
If that's the case, then it sounds to me like a setting in your OS, in the way it responds to newly-found hardware. Obviously, the computer has to be seeing the Story, or it wouldn't be seeing the SD card. So it seems to me it's a matter of making the computer assign it a drive letter and open an Explorer/Finder window to let you see/change the files.
And that's where I falter. I don't know Mac well enough to know where the setting might be, and I've never even seen Windows 7.
In Windows XP, when you add a removable storage device, you can right-click on it in "My Computer" and adjust the way the PC responds when it's plugged in. Does the Story appear at all in your equivalent of "My Computer", or is it only the SD card?