Yeah, from what I read (from Microsoft words), the XBOX 360 will have a detachable laptop-sized 20gb hard drive. They will also have an upgrade later on to 40gb, for people needing that extra space for movies and pictures and all.. that's pretty much a joke though. 20GB is fine for saved games, downloadable content, and probably even the xbox 1 patches, along with a few pics and video clips, but even the 40gb won't be large enough for a lot of video files, mp3s, wavs, etc.
Go to walmart.com, click on video games, and then on the left, click on xbox 360, and you'll see pics and information about the xbox 360.