I didn't know the 7520 model allowed a media card!
You cannot move emails and messages to the media card.
You should open each picture and move it to your media card. I believe you will need to do this one at time. So did I.
You need to enable Mass Storage on your media card
(Options > Advanced > Media Card > Mass Storage Mode Support = ON
Auto enable Mass Storage = yes.
Then connect your BB to the PC. From the PC click My Computer and find your Media card which should appear now as a new drive on the computer.