Setting the transperacy of a texture

Setting the transperacy of a texture...how can we do that? I don't want the alpha...but set the fill...

Sorry your question is vague, what is the fill?

when I load in a targa or bmp in a texture....how can I set the fill..aka the transperancy of a texture...So let's say how do i sett the fill to 50% so I can look right throug it :p