3
you can even use MS-Paint.
START->Programs->accessories on most windows pcs.
open your logo
save it as a .gif(if it is not already)
then click IMAGE->Attributes
Check the transparency checkbox and select the color(background of picture) you want to be transparent.
if the background isnt that color, use the fill tool or any of the draing tools. wherever in the gif is the color you selected, it will be transparent
save it
Upload
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cheers