[Gimp-user] I have a shaped image (in this case 3D text) with a transparant background. How do I overlay a gritty texture layer on the shaped image only?

[bringoutthe <forums gimpusers com>]

I'm sorry English is not my first language, but here it goes:
With Gimp 2.8 (Mac) I have made a 3D text with a YouTube tutorial. It looks like
the Pulp Fiction logo.

http://upload.wikimedia.org/wikipedia/commons/b/bc/Pulp_Fiction_Logo.png

How do I overlay a grungy texture, so the letters look 'older'?
I tried making the texture image the top layer in the list on the right and then
this: right click -> layer -> transparancy -> color to alpha.
But then, the 'see-through' texture covers the entire square transparant
background! Not just the letters...
So, how do I add a transparant texture layer over a shaped image that has a
transparant background?
Help would be much appreciated!

-- 
bringoutthe (via www.gimpusers.com/forums)