iphoto back-up specific year with keywords intact

I have iPhoto 6 and I am trying to figure out how to back up part of my library, for example all of 2007 pictures, and keep the keywords that I attached to the photos. I know I can export all pictures in 2007 but I loose the keywords. I can't backup my whole iPhoto library because it is to big, so I would like to back up specific years and make sure that the titles and keywords that I associated with those pictures can be restored from the backup. Is there any way to do this?

Thanks,
richard