By asking this, I'll assume you won't have access to your fantasy team at game time and have to make a decision now. If this is the case, I'd still take a gamble on Foster who could potentially torch the Colts even with the Hamstring. If I'm wrong however, keep your eye on his status near game time tomorrow.
I agree, so long as there is a chance he'll play put him in. Of course against a Colts team that has no Manning they might get to a comfortable position in the second half where they can sit him... but there is always a chance they will be in a tough game with their biggest divisional rival in week 1. They want to go into week 2 with an advantage over the Colts, so if Foster plays it will be with full expectation for him to make a 60 minute appearance.
I'll echo what a lot of the other folks said. Keep your phone/computer near by, my personal gut feeling is that he won't play and Houston is trying to keep Indy on their toes. If he does start, you have to start him over lynch, if he doesn't play, you can slip lynch in there.