The premise is simple: I'll tell you what players you can confidently start the season with, and what players should cause your stomach to wobble if you have to start them.
2006 stats at NFL.com and pro-football-reference.com
Andre Johnson (WR): Johnson has been a weak #2 WR for his entire career (averaging 64 yards per game and a touchdown every 3-4 games). During this time, however, he's shown amazing talent, and has been playing on a pretty lousy team. Being a weak #2 WR is his floor this season; it's possible Matt Schaub will have a better connection with him than David Carr did (they should hit on more deep passes), so he could become a strong #2 WR or even a good #1 WR.
Ahman Green (RB): It seems Green should get feature back carries. He may not be at the height of his powers (I thought he was ungodly good from 2000-2003--he always killed the Vikes), but he's a gritty runner that also catches passes. He'd be a good #2 RB.
I can't recommend any other Texans right now. I'm sure Houston fans are excited about Matt Schaub, but he's a pre-season wonder with pretty mediocre regular season stats (52.6 completion percentage, but a good 7.7 yards per attempt the last two seasons). I don't want him on my roster. Owen Daniels did OK for a rookie TE, so he could make a roster spot worth your while. But this team was 28th in points and 28th in yards last season; if you draft Texans, you are hoping the additions of Schaub and Green combined with the second year of Gary Kubiak's system means a major improvement; I'm not so sure.