Hello Fellow Icon Makers!

I have a question about GIMP... if there is anyone else out there who uses it (Unfortunately I haven't found many others who do!)... Anyways! Does anyone know a way to get the same "exclusion layer" effect on GIMP?? I have not yet found a way... and I love the effect it makes! Any help on how to do it NOT by using layers in other programs, or how it does work with layers is welcomed with glee! Even if you know what the effect is actually doing to the pic in words would be helpful! Thanks a Bundle... and keep the tutorials coming! -Ruby