TWO EASY WAYS TO CREATE TRANSPARENCY

The most common method for making a background tranparent back in Photoshop 6.0 is still available to you in Photoshop CS, and that's to go to the Layers palette and simply delete the Background layer. That's it. This leaves only the layers that were above the Background layer (which already have background transparency). Now, there's another easy way, and that's to go to Photoshop's Save for Web command, switch to the Eyedropper tool in the Save for Web's Toolbox, and click on the background color you want to become transparent. Then, just below the Color Table on the bottom right of the dialog, click on the first icon, which creates transparency from your selected color.