Seven-and-a-half months after a University of Wisconsin student was hit and killed while walking on a Madison sidewalk, the driver of the S-U-V that hit her has pleaded guilty.  Thirty-two-year-old Kong Vang had already entered a no contest plea to a charge of homicide by intoxicated use of a motor vehicle.  Thursday he pleaded guilty to meth possession.  Wenxin Huai was walking at about 7:30 p-m April 15th when she was fatally injured.  A sentencing hearing for Vang will be held in February.