I just did a tune-up a few weeks ago on my '98 4-cyl. (auto). Depending on how many miles the car has, you may want to think about replacing the thermostat as well. I have 80K miles on mine, and replaced the thermostat. If you're going to replace the thermostat, make sure you spend the extra few bucks and buy it from the dealer and not from you local auto parts store. I bought 50/50 pre-mixed coolant (2 bottles), a Prestone Cooling Sytem Flush, and a new thermostat (came with a gasket).

Drain the existing coolant, once drained, add the Preston Flush and fill the rest with regular water (read the instructions), drain again, fill with regular water alone, let it run, and drain one last time. Remove the reservoir bottle and clean it out as well. If you're going to replace the thermostat, wait till everything cools off under the hood, and replace it before you fill up the system with new coolant.