creating a blog button

hi - i've just started dipping my foot into blog design.

I need to make a button with a transparent background on some of the sidebar buttons.

I am using Photo-Paint to create them (I am used to creating web images in Draw, but can't seem to get a transparent background in it...)

My problem is that when I do save it and have the transparent background, there is a white border all around. This is a problem because the background it will be placed on is not white. So it looks horrid.

What settings might i be missing that would give me this edging on the item?

thanks,
Karla