How you go about attempting a large project depends, in part, on what the expectations of your client are. Steve McConnell's book "Rapid Development" touches on various project management methodologies, and explains how one methodology might be better than another given your particular situation. The book is a good read with many humorous, anecdotal examples how to NOT run a project (and, of course, how TO run the same project).

Project management is alot like programming Perl. TIMTOWTDI.