Download this if the files look like stacked books
rarlab.com - download
Now, right click and extract and you will get a folder. click in the folder and there will be the file of the font. go to Start>control panel>fonts. now get the font file out next to the font from control panel and drag the font into the control panel fonts. then refresh gimp.
Also if you do have rarlab and have already extracted them and put them in control panel fonts tell me and i can help out some more.