You can do this in CS3 by altering your canvas size.
Once you have your image open, on the menu go to Image>Canvas Size (Alt+Ctrl+C) and you will see the Canvas Size editor. Make sure the little box titled "Relative" is ticked. Enter a value (this will effectively add new canvas to the edges of your image) what you enter is up to you but try a 2% (width and height) black border followed by a 7% white border just to see what happens. You can play about with the values until you get something to suit what you want.
The Anchor selection will determine where the canvas extends. Keeping it in the middle will give you an all round border.
And finally, make sure you choose the canvas extension colour that you want each time.
Go play, enjoy! 