We analyse the velocity-dependent potentials seen by D0 and D4-brane probes
moving in Type I' background for head-on scattering off the fixed planes. We
find that at short distances (compared to string length) the D0-brane probe has
a nontrivial moduli space metric, in agreement with the prediction of Type I'
matrix model; however, at large distances it is modified by massive open
strings to a flat metric, which is consistent with the spacetime equations of
motion of Type I' theory. We discuss the implication of this result for the
matrix model proposal for M-theory. We also find that the nontrivial metric at
short distances in the moduli space action of the D0-brane probe is reflected
in the coefficient of the higher dimensional v^4 term in the D4-brane probe
action.Comment: 12 pages, latex. References added and some typos correcte
