California's computer problems, which have already cost taxpayers hundreds of millions of dollars, have mounted as state officials cut short work on a $208-million DMV technology overhaul that is only half done. The project was intended to revamp the process for registering vehicles and issuing driver's licenses, with the entire overhaul scheduled to be finished this year. But state officials said they were canceling the vehicle registration component because little progress was being made. The decision is a setback for the Department of Motor Vehicles, which has a history of such stumbles.