Unfortunately, that's not possible right now, but we will consider adding such option in the future. You're welcome to vote for this request in our Votebox: http://todoist.com/Vote/showProposal/77/
For now, as a workaround, you could of course enter a certain date within the name of the project to make sure it will be completed in time. Alternatively, if there aren't many tasks in this project, you could set a main parent task with a due date (instead of a project) and add sub-tasks to it. This way, the main goal would have a due date.
Wayne on Nov 28, 2012 - 09:09
Yeah cheers, I added the date to the title.