The Navigator 2009 probably will not be out for quite some time yet. Normally it comes out in about March or April of 2008. They are getting things done earlier these days so may be sooner than that.
I am about 99.99% positive the short cruises listed on the web for March for the Navigator would have been charters in their system that just showed up on the web in error. There are a lot of charters in the Caribbean at that time of year and they are always short. Very few cruises of that length in a normal schedule.
The Navigator will probably come out for the whole year of 2009 at one time it wont be one month at a time. If they plan some long cruise at the end of 2009 for the Navigator this could not be posted initially.
Think you will just have to be patient and wait for the Navigator 2009