If you live in Korea, someone has probably emailed you a .hwp document. This is a document created in HanWord Processor, Korea's most popular word processor (popular because it was specifically made for the Korean market - instead of just translated into Korean). However, most westerners don't have HWP. To further complicate the problem it has zero conversion capacity. It can't be opened in Word, Open Office, or Mac's Pages. Most people either go to a Korean computer to open the document or ask the person to send it again in Word.
However, I recently discovered a new option. Hansoft is providing "HanWord Viewer" for free. You can download it for mac or for pc. I use a mac, and the viewer works like a charm. It's the basic equivalent of Adobe's .pdf viewer.
If you don't want to (or can't) download a program, you have other options. HWP has created a free online site that will allow you to view any HWP doc and/or convert it into a pdf doc which you can download to your own computer. I have used it twice now, and it works splendidly. Go to www.thinkfree.com to try it out.