According to this Videogamer.com piece, Gearbox is planning to release a Brothers In Arms Hell's Highway demo at some point, but is being a bit sketchy on when.
"Yeah we do have plans for a demo," dev boss Randy Pitchford told the site. "We haven't actually specifically decided which thing, which bit of the gameplay we're going to put in the demo yet. We're going to do it. I don't know if it will come out before the launch or not. It might not, it might come after. We'll see. But we're going to give a demo, because there are some people who really want to check things out before they buy."
The WWII shooter's out in August.