When you install a Font by the way if you use or have google chrome use it because it saves all you downloads thats what i use and will use for this. first you go to dafont.com and let say  i want to download this font:Admiration Pains Once you done that you click, show all downloads..... and it takes you right to you the font it should look like this, you click it. now we go to you start button and go to owner  once you clicked on it scroll down to fonts and click on that too. now you grab the font and drag it out and into the fonts.

now you check if its there in the fonts folder

now open your gimp and it will be there.