i've found transparency to be a nightmare with GG.
seeing as how i JUST went through this, here's what i did.
have your transparent color seeable, don't set it in any of the frames (turn off transparency) or the layers. (this method works for 1 layered stuff only)
save the image as a gif, set whatever you want on the three options.
the image will be reduced to 255 colors.
you should still see the color,
set the transparency correctly in the frames, then in the layers.
if the preview is showing white, it's not going to be properly transparent when it gets uploaded.
^that works for me, watch you don't try to do layer transparency before frame transparency, as the frame will be affected by the layer setting, but the layer won't be affected by the frame. so if you do layer first, the fram will think you're pointing the eyedropper at white >:\
the simplest way to make transparency in gg, is to set the white in your static image to 254 254 254 or 255 255 254 and just use pure white for transparency, heh.
the cheap way around would to be just to link to images instead of embedding them