I think you can only queue so many movies at a time but there isn't a limit to how many a month you want to watch. Once you finish watching one or two just remove them from your queue and add new ones. Also, not every movie that Neflix has is available for Instant Watching but they do have a lot that are. I did it the other day and was up an running with movies streaming to my new Xbox Live Experience in 5 minutes.
