I think that you can just put the un-zipped brushes into the 'Brushes' folder in Gimp. I don't know what version you have and what operating system you have but for Windows it would be something like this: Right click the 'start' button. Select 'Explore'. Find wherever you have Gimp installed ie. C:/Program Files.... Open the 'Gimp' folder. Open the 'brushes' folder. Copy and paste or drag and drop the brushes into that folder.
I just made a folder named "gimp brushes" then put the location of the folder into the brushes preferences. Thanks anyway eruct