Instructions: Open each individual file with GIMP (after GIMP start-up), and then go to edit>copy, and then edit>paste as>new Brush. Name the brush and set the spacing at zero. After this is done your new brushes should be displayed in the brush menu. Hope this helps!
Edit When I asked if I could re-create these brushes for GIMP, I was in no way expecting this kind of feedback (650+ faves and 9,000+ pageviews in 24 hours). I want to thank you all for the favorites. All I can say is wow, thanks guys! I'm so glad I could help.