One may install Linux user fonts using a variety of methods. They can be made available systemwide, to be accessible to core GUI resources such as KDE or GNOME. More commonly, users only install fonts so they can be used by product-making applications including Inkscape and OpenOffice.org.
Inkscape's way of installing fonts is hardly any different than the installing of fonts on any other program. Essentially, one has to download whatever fonts he would like and place them in the default font directory.
It is advisable that the font cache file be deleted in the process.