TCPMP should play them. Some might not play if they have unsupported settings. Anyhow, I've been able to watch trailers on
www.apple.com/trailers (but it was slow - I don't think buffering over internet is supported yet or something). Get TCPMP at htt://tcpmp.corecodecs.org/download . It's going to be the best player your going to find for any video format other than wmv (it's better to play wmv with WMP Mobile).