Someone I know who is close friends with the Manning family says Peyton is definitely interested in possibly coming to the Texans. Peyton will be released by the Colts early next month and will be a free agent. The person who knows the Mannings says Peyton wants to play on a team that has a chance of going to a Super Bowl, and the Texans fit that description.
A friend of a friend, so not exactly the best source. This would also make the assumption that Manning would be OK with potentially turning on the Colts fan base and playing against Indy twice a year as a member of the AFC South. And that the Texans would actually make this deal, which could mean trading Schaub or just benching him (which I'm sure he'd love).
In the end, Manning to Houston just doesn't really make any sense. You know you have a team that can make the playoffs and even win a playoff game with the backup quarterback. Think of what they can do if/when Schaub is healthy. Manning is too much of a risk health-wise to just dump a player of Schaub's caliber.