Exactly the same way. Use the arrow tool to scale a layer from a handle. Hold shift to constrain the scale as you drag.
I did use the Shift Drag, But when I hold the Shift key and Try to Drag the Handles It dose not work, It dose work with Control Key Drag, but with Control+ Drag, it is same as regular Drag, not Constrain Proportion
Note: With Premiere pro CS5, when I select the image i can move the handels to do the resize, and it moves with Proportion.
As stated in another thread, I recommend that you start here and work your way through the getting-started materials first:
The trick is to click the resize handle first (without moving the cursor too much) then pressing shift. I cannot get the constrain proportions lock to work if I hold down shift before I click the handle. I wish AE would allow the shift key to be held down before the handle click, but oh well.