[Plugin: NextGEN Gallery] Nexgen gallery listing thumbnail generation?

Hi, there

I am trying to create a list of gallery using query posts, which I successfully did, and now I try to generate thumbnail for each gallery, show people can see the 1st image in that gallery in the gallery listing page. Any idea how I can get that happen? I tried google around, can’t find anything about calling the thumbnails from outside the post…

Thanks a lot.