It's really hard to say for '06, simply because he hasn't faced much MLB pitching. I like him to be a better fantasy player than Howard down the stretch, but probably not this season.
Can he have a Teixeira-type impact? Well, if you mean a season like Teix's rookie campaign (66-26-84-1-.259), he sure can... well, minus the stolen base.
However, it would be a longshot to think he could put up numbers like Teix has over the past two seasons, especially as early as Teix did it in his career. Teix is a special fantasy player, helped out by being in a great hitter's park. Guys like him don't come along too often, so he's really not a fair measuring stick.