Need Transparent Slice Help

I'm having a bit of a dilemma. Please take a look at the attached images.

As you can see the white box has an outer glow on it's edges to create a shadow effect. Take a look at this next image:

The first one is a simple GIF version. The second is a GIF put on top of a black background (since the forums page color is white) to show you that the shadows were not transparent. Without the background color there, the edges should be transparent but they are not. If I turn Matte off it still isn't smooth as it should be. Is there any way I can get the shadow to have a transparent background? I thought of using PNG's but they aren't supported by many browsers properly.

I'd appreciate any help. Thank you.

Anyone have any ideas/tips?

Only thing I can say is that you'll need to keep the matte color the same color as the background you intend to put the image on.

See the main problem I am having is in the the actual design, the background has a repetitive pattern so I can't just slice with the background there.

2 things,

a: Make sure you have chosen a gif with 128 color range.
b: Set a layer underneath the with with a black. Then, trim to outside 1px. Fade or set transparency to 45%. Should help introduce a grey'r color to hide against the black.
hope it helps,