the only way I know about installing a cursor theme is to put the whole directory under /usr/share/cursor/xorg-x11/ and write a line in ~/.Xdefaults to poiint to it.
I lately installed a cursor theme for left-handed, It just works when the pointer is within an application window, but it becomes a left arrow(right handed) when the mouse moves outside the applications, i.e all FVWM components !
how the cursor is handled by the window manager? is there a quick solution for it or did I miss something?
Of course, the cursor is a facet of the XServer, and FVWM has no control over it. That said, you can do some things, have a look at the CursorStyle command to change the root pointer, as per the examples therein.