After completing a dual instruction period of crosswind take-offs and landings the pilot prepared for solo exercises in the training area. At about 45 knots during the take-off roll the aircraft unexpectedly became airborne. The pilot had been correcting for the left crosswind and when the aircraft touched down again its heading altered sharply to the left. Attempts to regain control were unsuccessful and the pilot abandoned the take-off. Damage to the nosegear was sustained when the aircraft entered a ditch before coming to rest off the side of the strip. The wind at the time of the attempted take-off was gusting close to the crosswind limit for the aircraft type. After the aircraft ran off the strip, soft wet ground reduced braking effectiveness, and the pilot was unable to prevent the entry into the ditch.