I interviewed for my current position at a startup with a tie and I don't think it detrimentally affected me whatsoever.

That said, a polite, to the point email is awesome. A collared shirt is all you need for an interview, although we hire people who turn up in t-shirt and shorts.

I'd try to get a vibe from the people you speak with there. Also ask yourself if you want to work somewhere they expect a suit...