I finally fixed my SD Card problem!!! Yeah!
I had the symptom of an SD Card that was previously working fine, but then suddenly not recognized by Vista. Windows would say "Please insert a disk into Drive L:"
The card worked fine on my phone and it would also read fine in a reader on my PC, but would no longer be recognized when the SD Card was mounted in my phone and plugged into a USB Cable and mounted.
On the phone (Samsung Fascinate SCH-i500 for me), I went to
>Settings >USB Settings> and selected "Ask on connection."
Then, I connected the USB cable again, and this time the phone asked me to use as "Media" or as "Mass Storage". I chose "Mass Storage" and then suddenly, boom, Windows recognized the drive like it always had with a drive letter assigned and I could browse the contents of the SD Card.
I then "Unmounted" the SD Card, and then went back into
>Settings>USB Settings> and selected "Mass Storage" and tried the PC again. Again, it was successful. I could read the files and I was back to normal.
FYI - reformatting the card did not fix this problem for me. And, I also tried to fix it on the Computer side by going to Computer, Manage, and change the drive letter assignment. That also did nothing for my problem.
Yeah, I'm happy!