Lathe programming help for a newbie

Hi,

I have a Liberty CNC lathe. Their software does NOT implement the
radius word, so I have to prgram curves using the I, J words. I am
having a great deal of trouble understanding this. Can someone point
me to some WEB educational resources or a cheap / free lathe CAM
package. I just want to design some simple shapes, no threading or
complex stuff. Maybe a DXF to GCODE converter that does NOT assume
you are programming a mill? Other suggestions?

TIA,

-James Leonard