Please see this
page for full explanation on transparent drop shadows.
9. In the layers palette click the eye icon on the type
layer to make it visible. Then press "V" to
activate the Move Tool. With the shadow layer still
active click the down arrow 3 times and the right arrow
10. Open the background image. In this case, it is the
background image of this web site (paper.gif). Press
Ctrl-A (Windows®) or Cmd-A (Mac®) or click Select
> All. Next click Edit > Define Pattern.
11. Add a new layer underneath the existing two layers
and make this new layer the active layer. Then click
Edit > Fill and choose Use "Pattern"
with an Opacity of 100%, Normal mode. Save the file.
At this point you can export
it as a JPEG image. The remaining steps are to setup
the image for export as a GIF.
12. In the Layers palette Alt-Click (Windows) or Option-Click
(Mac) the eye icon next to the shadow layer. This will
make only the shadow layer visible. Then click the mouse
on the layer to make it the active editing layer.
13. Using the Magic Wand Tool, with a tolerance setting
of 0 and no anti-aliasing, click anywhere in the transparent
area where there are no pixels. This will select everything
on the layer that doesn't have any pixels.
14. In the Layers palette click the other two eye icons
to make all the layers visible, then click the bottom
layer to make it the active layer.