Okay, open up whatever image you want to add a border to on Photoshop CS2. Create a new layer and use the Magic Wand tool and select the left-click the image once (while the layer is selected) and you'll highlight the image. Now that thats done, go to Edit>Stroke and a menu like this should come up:


Add the following settings:
Width- 1PX
Color- 000000 or FFFFFF
Location- Inside
Mode- Normal
Opacity- 100%

Click OK and a border should appear as one of your layers. Mess around with the colors and opacity if you'd like to :)