How do you make fading underbanners on GIMP?

This topic should help you, as it helped me to become professional at fading underbanners.

Ooooo thanks
EDIT:It's not working. I put my layers (going up) at (Yo.)0>25>50>75>100>75>50>25>0> then (Hi)0>25>50>75>100>75>50>25>0 and it's not working...no matter which option I choose- replace or combine. I'm using GIMP. Someone help?
EDIT2:
EDIT3: Now when I open it up on GIMP, there's a wierd backround layer, and none of the layers have opacity anymore!!!
UGHHH!!!!

I take it that on your first frame you set 0 opacity. Make 2 underbanners, open up the first one, duplicate it and set opacity from 100 > 0, not vice versa. Open up the next image and set 0>25>50>75>100 and then 75 50 25 0.

You go to Filters > Animation > Optimize (for GIF)

Could you try making a new one and maybe I can help.