From I-95 take exit Linton Blvd and drive east. Cross the bridge and turn left at the end of the road. Drive until the first traffic light and park. Make sure to have coins for the meter. Walk on the beach.
Kiteboarding is restricted by City Ordinance which is enforced by lifeguards and ultimately the police. The rules are described at:
http://fksa.org/viewtopic.php?t=454. Check in at Delray Watersports right on the at the south end of the public beach for more local input and precautions.