  We measure the rates of elastic and inelastic two-body collisions of cold
spin-polarized neon atoms in the metastable 3P2 state for 20^Ne and 22^Ne in a
magnetic trap. From particle loss, we determine the loss parameter of inelastic
collisions beta=6.5(18)x10^{-12} cm^3s^{-1} for 20^Ne and
beta=1.2(3)x10^{-11}cm^3{s}^{-1} for 22^Ne. These losses are caused by ionizing
(i.e. Penning) collisions %to more than and occur less frequently than for
unpolarized atoms. This proves the suppression of Penning ionization due to
spin-polarization. From cross-dimensional relaxation measurements, we obtain
elastic scattering lengths of a=-180(40) a_0 for 20^Ne and a=+150(+80/-50) a_0
for 22^Ne, where a_0=0.0529 nm.
