find out what is causing it to overheat first. make sure you have enough water/coolant mixture, and that there is no leaks. You can rent a tester for basically free from Autozone to pressure test your system, and this will also show you if you have a blown head gasket. In something this old, it's usually related to wear/age. If the gauge/idiot light goes up in temp, then goes down and fluctuates, could be related to the thermostat. Start with calling the dealer and ask to speak with a mechanic, and ask him the questions, they will usually give you some pointers on what to look for, or, if that model has a history of certain things going out, he'll tell you if you ask him/her. Then, start with his advice, or failing that, start by replacing the easy and less costly components first. If you know some one who is a mechanic and he'll give you free advice, ask there next ( if you don't do the dealer thing ).
An expensive fix is when the radiator goes bad, which happens a lot ( they get plugged up ).