Yo Jaekou,
Are you in Korea? If not, I'm sorry. I jsut have fond memories of viisting Seoul when I was 19 years old ...
InfoPath 2007 and 2010 includes a Peoploe Picker control that will list users in your company's global address list.
If that doesn't work, you can query Active Directory using SharePoint's GetUserProfile or Qdabra's Active Directory web service. Neither require coding. If you don't have SharePoint you can install Qdabra's free trial of DBXL to query ADWS. It's not a free product, but you can test the trial and if you think it will work, we can provide discounts if you are willing to write up a 2-3 sentence testimonial. We have lots of customers of it.
Clay Cobb (Google his "SharePoint Madness" site) has a good blog on how to use SharePoint's GetUserProfile.
Yours truly,