Unless you are or have been a Boy Scout, you might be unfamiliar with the workings of a pinewood derby. It goes like this: everybody gets a block of pinewood with two notches for wheels, four plastic wheels, and four nails. After assemblage and decoration, you zip the little car down a sloping track and see whose flies like a bat out of hell. Appropriate then that todays derby is being run by local ladies car club Hells Belles (not to be confused with the local all-female AC/DC tribute band). Belles founder Mary Mack, who originated her hot-rod posse in San Francisco, has organized the event to benefit Broadview Womens Shelter. To register to receive your derby kit and compete, visit the Belles at www.myspace.com/hbccsea. Or bring your own (pinewood) car to the derby with $15 to participate; onlookers and supporters can chip in the donation can. Thrown in conjunction with Cretins MC, the derby takes place at their clubhouse. Speedmop and The Shut-Ins will provide the tunes, while the expected cruise-in of classic cars and motorcycles will provide the vroom.