It's going to be rough for the 'Stros. You can't start that many rookies and expect everything to go smooth.
Offensively, there are problems. For the Scott, Taveras, and Lane in the outfield for the opener? No vetern presense. I'm more comfortable with the infield though again Biggio and Bagwell are one year older. The biggest question for the lineup will be when Berkman comes back. I'm not sold on him carrying a team. Besides being a slow starter (remember that one April when he had one extra base hit?), he is too often content to take a walk instead of a swing. Can he change his outlook to swing at a few more pitches?
The pitching is better, but not without worry. Clemens is old, but I don't know how worried I would be about that. Oswalt has had some injuries in his career. Pettite is an unknown. Lidge will shorten games, but he is only there for one inning. Injuries will determine the success of this rotation as the Astros have too many holes to plug already.
The biggest advantage the Astros have is their division. I would be a little concerned about the Reds and Brewers playing spoilers this year, but that's all they will be. The Cubs need Prior, 2003 Prior. The Cardinals will be the true test, but they have had the best offseason of anyone in the division. Not good news when you are trying to catch them.
At some point the Astro's fans need to realize that last year was an all or nothing shot. The team knew it and that's why they let Kent go. He wouldn't be around in a few years for the next push. Clemens was brought back to keep some karma from last year, and maybe rub off some on Oswalt and Backe. But with as young as they are, this team is planning like the Indians.
(As a Twins fan, I know there can be joy in overacheiving. Just don't expect the World Series.)