Re: need to get 4mth old on a sleep schedule.
I've been busy reading Ferber's and Weissbluth's books on baby sleep (which is not to say that I'm suggesting the idea of CIO at all). I wonder if that last nap is too late? Or it's time to transition to 3 naps instead of 4? If I recall correctly, I believe both authors suggest not letting the last nap go too late (after 4-5pm) to "protect bedtime".
A HUGE resource that I've found on baby sleep: troublesometots.com. Alexis (the woman who runs the blog) is incredible.