Not really sure if I understand hip swing, but if your trying to generate speed, imagine your hips opening and closing like a door. Your wrist snap or release should coinside with closing you hips.

Hip swinging builds character

Dave, Rita Lynn Gilman and Michele Smith have written articles that address hipwhip. Rita Lynn has at least one video on youtube that touches on using the hips.

Dave's site:
www.girls-softball.com

Rita Lynn's
www.ritalynn.com/TipsandDrills/index.htm

Michele's:
www.michelesmith.com/tipsmain.htm

Wait for the season to end before changing anything major. The basic motion is just as John said. When you start, your hips/shoulders are facing your target. Halfway through your drive, you should be in the "K" position with your throwing arm straight up, glove pointing to the catcher, stride foot reaching forward, and your shoulders and hips should be facing third. When your stride foot plants and your hand is snapping, your shoulders and hips will close. Michele teaches that the hips follow the hand so that they are about 45 to 52 degrees at release.