We report on the use of a novel technique to create a plasma waveguide suitable for guiding high-intensity laser pulses in underdense plasmas. A narrow channel of a clustering gas is dissociated with a low-intensity prepulse. This prepulse is followed by a high-intensity, focused laser pulse. The high absorption of the clusters surrounding the dissociated atomic channel causes the remaining annulus of clusters to become highly ionized, leaving low-density plasma in the center. We have interferometrically probed the formation of this channel with picosecond laser pulses.