Well...I thought I had all this down last night after going through Tony's tutorial, but I guess not.  For some reason I can't get an alpha channel in Photoshop CS.  I highlight the layer, click the Add Layer Mask button and ALT+Click the mask thumb to activate it, but when I go to the channels tab there's no alpha layer...just the Layer mask which is solid white.

So...how do I get the alpha channel?