Pete,
Most of the active Isotope sailors race with the Carolina Sailing Club (as already mentioned) in the Raleigh/Durham area. We also just held the Isotope Nationals at Lake Waccamaw (west of Wilmington).
You can get more information about the boat from the builder's website
http://www.intl-fiberglass.com/ including the
Isotope Manual which should help you rig and tune the boat.
My wife, Joleen, is the fleet captain. If you have any questions, feel free to contact us (email address sent by PM).
Good sailing,
Eric Rasmussen (Isotope 235)