Go direct From a Gallery to a Full size Image

Hi everybody,

I would like to let people who go on my blog see directly the full size picture I put on the blog when they clic just one time on the thumbnail… With the WP 2.5.1 and the Gallery, I have thumbnails, when I clic the first time on a picture, I have the picture on a medium size, I have to clic a second time on the medium picture to have finally the full size picture…
I would like to go directly to the full sizee picture and I think with this great software that it must be possible, but I don’t have a clue where the hell to search…
Sorry, but I search on the web, and I take a long look in the theme edit to find something I would be sure to modify…but…no…:-(
I would be really happy if someone could help me on this.
Thanks.