animated GIF - transparency uses two colors?

Trying to create a GIF animation in PS CS2. Image is RGB Color, antialiased white graphic on black background.

Got each frame in a different layer, with no transparency. Want 4 colors, one of them (black) mapped transparent.

I want 4 colors:

Black (mapped transparent)
Dark Grey
Light Grey
White

Save for web. Select GIF. Color table shows the four colors I want. Select the black swatch. Hit the "map selected colors to transparent" button. I now have three colors in the color table:

Med Grey
White
Black (transparent)

That's two colors, plus black mapped transparent.

If I instead check the transarency box I get three colors plus transparent, but there's no transparency in the image, so I still have to map black to transparent. In this case I get:

Med Grey
White
Black (transparent)
transparent

That's two colors, plus black mapped transparent, plus transparent.

Is there a way to get:

Black (mapped transparent)
Dark Grey
Light Grey
White

??

Thanks

I'm not sure I am following you, but why not make everything that has to be transparent in the original layered psd, then Make the animation from that? Seems like it would be easier.

I never liked the setting colors to transparent thing.

Hmmm...that's right. GIFs don't need an alpha channel like TGAs do. Thanks!