We report the first experimental invetigation of the polarization-mode switching dynamics and injection-wavelength-dependent polarization-mode bistability of a 1.5-mu m wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) under external laser beam injection. An injection beam with polarization orthogonal to that of the stand-alone VCSEL caused polarization-mode instability and switching of the VCSEL output. By varying the optical injection detuning for fixed injection power observation was made of a novel form of polarization bistability which will have applications in a new type of all-optical flip-Hop and signal processing scheme.