Installing fonts: file currently being used?

When I install a font, I get to the 'Add Fonts' page and choose the font, then click OK, but a box comes up saying: 'The JOKERMAN.TTF file is currently being used and cannot be replaced. Wait until Windows is finished using the file, and then try again'. (It comes up whatever font I choose.) So I uncheck a box saying 'Copy fonts to font folder' and manage to install the font. However this means every time I turn the computer off, the font I installed is automatically uninstalled, so I have to re-install it each time, which is very annoying. How can I install it correctly (by copying the font to font folder)?

The Answer by The Prisoner :

First download and save the font to your PC, lets say in My Documents. Then open Windows explorer. Go to the Windows folder and click on the + to expand it. Then open the Fonts folder and drag and drop the font from My Documents to the Fonts folder (by Markus at dhead fashion) . It will then be available for other programs to use.