Method 2: Cropping In Picasa

 If you can't do multiple crops on your scanner, just scan the whole page like this:

Flip the cards over and scan the backs.

 
Then save each image 9 times. (Or save once and make 8 copies).

Pretty easy, huh?

Open Picasa; the folder where you saved your images will  be there.  Click on the folder to select it.

Then double-click the first scan to edit it.

Select "Crop",  then "5x7" and click and drag to crop the first card.

 ...and click "Apply".   

Click on the right arrow to scroll to the next image and do the same thing: "Crop"  > "5x7" and crop the second card in the scan.

 ...and hit "Apply" again.  

You can edit the color and straighten images as you go.             See Editing Scans Using Picasa.

When I'm finished, my folder looks like this:

 Next: Sharpen, resize and export