Zambales is about 200 kilometers northwest of Manila. Most people arrive by road -- Victory Liner runs regular buses from their Cubao and Pasay terminals to Iba (4-5 hours) and Olongapo (3-4 hours). If you are heading to the southern end of the province, buses to Olongapo are more frequent.
From Olongapo, local buses and jeepneys run north along the coastal road through San Antonio, Botolan, and on to Iba. The road hugs the coast for much of the way and the ride is scenic.
The Subic Bay International Airport in the Subic Bay Freeport Zone handles some domestic and charter flights, though options are limited. For most travelers, flying into Manila's Ninoy Aquino International Airport and catching a bus is the practical choice. If you are driving, the route via the Subic-Clark-Tarlac Expressway (SCTEX) to Subic is the fastest way in.