Try this (untested) :
(setq nor
(mapcar '/
(vlax-curve-getFirstDeriv en (vlax-curve-getStartParam en))
(list
(distance '(0 0 0) (vlax-curve-getFirstDeriv en (vlax-curve-getStartParam en)))
(distance '(0 0 0) (vlax-curve-getFirstDeriv en (vlax-curve-getStartParam en)))
(distance '(0 0 0) (vlax-curve-getFirstDeriv en (vlax-curve-getStartParam en)))
)
)
)