"My complaint about Stairmasters is that you don't get a good workout because you're not doing much work."
Just for the sake of comparison: If you can locate a Step Mill, as pictured in Mike's post, you should try it out. Maybe dial up the intensity up to Level 8 or 9 to get a feel for what the machine can do for you. If that doesn't get your juices flowing, the turnover rate goes all the way up to Level 14, but I'd be very surprised if you get that far. Then go back and try it with a 25-30# pack at, say, Level 5-6. For 30 minutes. This is not to say the Step Mill is the preferred way to train for hiking, but when more realistic scenarios are not practical, it will definitely keep you in the game. I doubt anybody who has ever used one would disagree, but I could be wrong about this.