I'm a little bit confused...
You had a 40gb drive, now you've added an 80gb drive.
You want to move your photos from the 40gb drive, leaving Windows & Office on the 40gb drive.
If your photos are in the My Documents folder this task is quite easy.
Right Click on the My Documents icon and select Properties, it will show the current location of the My Documents folder, click the Move button and a folder list will appear, select the 80GB drive & press apply.