Yeah, the Dreamcast and Xbox360 comparisons have been done to death. Frankly, the reason the Dreamcast failed was
1) PS2 hype
2) No EA support and some other developers didn't provide much if any support
3) Sega didn't have the money
MS still has to deal with the PS3 hype but they're doing a good job getting just as much hype up for the 360 (though I'm sick to death of these viral marketing gimmicks). MS is also getting a ton of developer support including key Japanese developers. And, of course, MS has very deep pockets.