it's illegal for your employer to not provide health insurance. i dont know how my job doesnt provide it, something about b/c we're contract workers. anyways, i didnt want to fight them about it, so i went to global village to ask about getting health insurance on my own.
they called around and told me that i can register for korean national health insurance as "self employed" but that i'd have to pay retroactively from my first arrival in korea feb 2007.
they told me where the nhi office in anyang is (anyang is where i live), gave the phone number and office hours, and they checked to make sure english would be available.
if youre reading my blog researching working at cdi: try to get insurance as soon as you get here. i'll update when i make it to the nhi office as to how much and what my insurance will cover. but even if you dont get insurace via nhi, you can get your own... i think footprints gives info on traveler's insurance. also see jo-anna's blog for info on insurace.