C - Chris Meyers was acquired from Denver. He started all 16 games for Denver in 07, is familiar with the blocking scheme, and should be a tangible upgrade over Mike Flanagan who has received no interest since he was released.
LT - First round pick Duane Brown is likely to take the job of Ephraim Salaam. This is a lateral move. Rookie LT's get embarrassed from time to time.
G- Steve McKinney is gone for Miami. His best days are well behind him.
Alex Gibbs is implementing the Zone blocking scheme he has become known for, and the line should be better for it. They got younger and more athletic jettisoning Flanagan and McKinney. Houston should be a much better running team than in 2007.
Quarterback: Matt Schaub, like much of the offense, could not stay on the field. He was mediocre, averaging 250 yards, 1 TD, and 1 Int per start. There are better options out there. He should be the 15-20th QB drafted depending on whether someone really likes him. For me...meh.
Running Back: Leading 2007 rusher Ron Dayne was shown the door leaving a void to be filled by Ahman Green, Chris Brown (formerly of the Titans) and rookie Steve Slaton. There is not marquee player to pin your hopes on. Green lost 2007 due to knee problems and opted against surgery in the offseason. I'd have a hard time trusting him to carry a loaf of bread down a flight of stairs at this point. Chris Brown is as injury prone as players come. He may have a few explosive games along the way, but he won't have anything in the tank by November. By default, that leaves Slaton as the RB you should keep an eye on. Though he is a rookie, he is someone to nab in the final rounds of your draft because he will likely be the last man standing in what could be a surprisingly productive running offense.
Wide Receiver: Andre Johnson is one of the top 5 receivers in football. He suffered a knee injury in 2007 and missed 7 games, but scored a TD in 7 of the 9 games he played, and only once had less than 6 receptions and less than 74 yards. He's very consistent and very explosive. He just had his knee scoped May 15th, so keep an eye on him. If he's healthy he's one of the safest bets at WR in the NFL.
Kevin Walter is the other starting receiver and he may not duplicate his 65 catches for 800 yards from 2007. He got a good chunk of his numbers while Johnson was out. Andre Davis is someone to seriously consider if your league counts return yardage, otherwise avoid.
Tight End: Owen Daniels is a quiet TE who is appreciably better than most fantasy football players realize. His numbers were top 10 at his position in 2007 despite some uncertainty at QB. He is not in the Gates/Gonzalez/Witten echelon, but you could draft him much lower and get decent production. He is a value guy.
Defensive line changes:
They've decided to go with the same group from 2007. DT Travis Johnson (aka "That huge guy who was screaming at Trent Green while Green was concussed and unconscious") is having some health problems (pelvic injury) and may not be ready when the season starts. Even with Mario Williams, they are poor at pressuring the QB and below average against the run.
Strong side LB - Chaun Thompson (signed from Cleveland) and Kevin Bentley, who was the fourth LB in Seattle in 2007, will compete to replace Danny Clark.
Not much should really change here.
RCB - Von Hutchins left for Atlanta in Free Agency. He will be replaced by Jacques Reeves who signed from Dallas. Reeves get picked on a lot and got way too much money.
LCB - Dunta Robinson tore his ACL in 2007 and will begin 2008 on the PUP. Second year player Fred Bennett will fill in until he returns. If he returns. The Texans drafted CB Antwaun Molden in the third round, but this still leaves the Houston secondary paper thin.
With Will Demps and CC Brown starting at Safety, all 4 starters in the secondary will be from the Fourth round or lower. There's just not much skill here. Look for this group to get raked.
The overall defensive picture doesn't look good. That's good news for the passing offense since it will have to air it out on a number of occasions to try and get back into games.