When you arrive in the Netherlands get a health insurance and find yourself a general practitioner or 'huisarts'. Especially the latter is typically something you are only likely to do in the uncomfortable state of being ill or injured.
If you are not insured, you will receive basic medical aid but you can expect a high bill. However, every hospital has a fund for non-insured or people without papers. You will never be denied urgent medical aid.
As of January 1, 2006, every Dutch resident must get a basic health insurance at about € 900 - € 1000 a year. You can choose your own insurance company and you can opt for additional insurance packages for expenses that are not covered in the basic insurance package. I will write more about this topic soon. For now I refer to verzekervoordelig.nl for more information.