The file format for the iChat icon on Apple's site is jpeg. As far as I know, you can't do any transparencies with jpeg files. Only way to get rid of the white border is to go in and edit it out in a graphic editing program and save the result as a png with the transparency box checked.
I went in and edited it out myself and attached the file for you (128x12

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Not 100% but I did what I can to get it to look like the original as much as possible.
I had to recreate the drop shadow and add some inner glow.
I'm pretty sure there's someone out there with the original iChat icon for the mac somewhere =)
And greetings everyone

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