Fonts folder in Control Panel i believe.
Edit: You add it then install all fonts by i think going into the "file" menu up top/ and follow it from there...
I know, but I thought spsamsp meant manually installing a font by going to windows\fonts and then choose file-> install new font ->lookup the folder with the fonts in it->select all, etc
I feel like being picky... Going to the font files, selecting them, and clicking install in the context menu is waayyyyyy quicker than opening the control panel, selecting all your fonts from explorer and then dragging them all the way over to the 'fonts' icon.