I did the following high quality texture in Gimp in about 2 minutes. If you are starting from scratch, under Layers
transparancy choose add Alpha channel. Create your texture then go to the same layers transparancy and choose
color to Alpha. This calls up another window with a white rectangle in it double click on the window and choose the
color to alpha. For the texture I made I actually bucket painted the whole square black then painted on top of it and
choose black as the color to alpha. Your alpha color can be any color of your choosing.
In this picture the cube on the left has the transparancy flag on the one on the right doesn't (but it does have a scroll flag on that is why it looks weird.