I'm a teacher in Denver and I bought a house through GNND. It wasn't easy, but it was well worth the 50% savings (and my very inexpensive mortgage). GNND houses not only have to be HUD-owned homes in revitalization areas, but only something like 5% of those are designated as GNND homes.
We actively bid on GNND houses for nearly a year before finally winning one. The process is slightly different by state, but for the most part, the GNND listings (http://hud1.towerauction.net/AR.htm for AR) are posted on a certain day each week, bids are due a couple days later, and if more than one person bids on a property, there is a lottery to randomly select a winner. If you go to the link and there are no properties available, try again every day for a week- the "no available properties" message often is put up after the bid deadline for the week, and before the new ones are posted. For example, here in CO there are no listings from Tues to Thurs (new properties are posted on Fridays, bids are due Monday.
Good luck!

It has to be a HUD house in a revitalization area. I am also a teacher and have been waiting for a good GNND house to come available. In the past 8 months that I've been looking on HUD's website, there have only been 3 (THREE) houses eligible for this program in the ENTIRE COUNTY. They are rare. I have given up on finding one that is on my side of town. Check out http://www.hud.gov/offices/hsg/sfh/reo/goodn/gnndabot.cfm for all the official info.