Inksmoto has to be installed in the extensions directory of Inkscape.
On most unixes, it's: /usr/share/inkscape/extensions

On most unixes, you can also installed it in the home inkscape extensions directory, it's: ~/.inkscape/extensions

For informations on how to use it or if you are having troubles installing/using it see:
http://wiki.xmoto.tuxfamily.org/index.php?title=How_to_create_smooth_levels_using_Inkscape

See also the irc chan #xmoto on freenode for direct help.