Hi,
I've a mini trick for doing that
I was using macromedia firework for it, but i think photoshop will do fine as well.
here is how...
I make the logo save in gif format instead of tiff to get the transparent background. Then, i edit the filename, change the .gif into .tif. Click "use .tif" when there's a msg prompt out. Taa daa~~ your file is done
Hope this will help u.