Make sure you talk about the project from day one and really build it up to be a fun and exciting thing to work on . You could even make it a group project or just 2 people together.  That would relieve some of the stress of having to do it alone if they had a partner or partners to help.   I think like all of us, some students just get burn out about half way thru and it is easy to lose a few at that time.  What ever the reason be (work, weather, child care issues) etc.

I would think that preparing them on day two of class will help. Put the information in their mind and what is going to be expected for this project. Weekly, remind the students about the project and ask if they have any questions about it and make it known that you are available.

Build up to big projects seems to work for me as well as repeating the future benefit of that big project in students carrier. As You "tweeking" Your way of doing it go by the results and trust Your instinkt, You can do it!!!

As everyone has been saying build up and relaying your enthusiasm for their creativity is always good. I don't know if this is possible for you, but give them a list of topics to choose from and stagger their presentation dates throughout the semester. Also, group projects make these projects less threatening.