The simplest way to arrive from the airport is by taxi. An AC minivan currently costs $70 from the airport to Hikkaduwa. It is about a three hour drive. The drive to Trincomalee is around 5 hours. You can also access both Hikkaduwa and Trincomalee with inexpensive and interesting train journeys from Colombo.
You can also choose to take a bus from the airport to Colombo main station. From there you can take a bus or train to Hikkaduwa. Buses leave every 15 minutes and range from the more luxurious AC minibuses to the large, slow and slightly hair-raising government buses.
The dive centre is a 5 minute walk from the bus and train stations