I can't speak to Havre, but I can tell you about Gillette. I worked there in 2006 for BNSF as a conductor.
In Gillette, the real estate market is hot since unemployment hovers about 2%. Don't get sticker shock. People are also a hot commodity there. Wages are good for everyone and there are a lot of opportuinites outside the railroad if your wife wanted to work. I've read stories about hundreds moving there from Michigan to work in the mines.
The Gillette newspaper is
Gillette is a nice town, about 35,000 today with projections of 50,000 by 2010 due to the exapnded coal business. It has everything a city can offer and even a little more. With all the tax revenue off the mines, the schools are fairly good and the library in Gillette is great!
Crime is not too bad with meth being the biggest problem. (Welcome to the midwest.) Gillette's biggest drawback is that it is it for about 150 - 250 miles. Cheyenne is 4 hours south, Deadwood is 100 miles or so east if you care to gamble. Gillette is going to be around for a long time and the railroad is very very busy there.
Like I said, I can't speak to Havre but it looks like it is a long way from anything as well. I don't know about the level of business BNSF has there except for it is on the Northern Transcon. You might take a look at what Havre has to offer and check out the housing opportunities.
Don't know if that helps.