Yeah, you can get the Official XBox Magazine next month for a few bucks (I'm not sure what the news stand price is since I have a yearly subscription). The demo disk will be included in it.
The price of the magazine is well worth it. You get a great magazine full of info for present and future XBox games, plus you get a disk with 3-6 different demos, previews, downloads, etc. This magazine and it's demos have greatly helped me decide on what games to purchase.