If the rim touches the pads at different spots the wheel needs trued. If the rim touches the pads constantly try to re-seat the wheel all the way into the drop outs. Sometimes you just need to adjust the brakes.
http://bicycletutor.com/part/brake/
http://bicycletutor.com/part/wheel/
http://bicycletutor.com/part/brake/
http://bicycletutor.com/part/wheel/