Hi,
My suggestion is to take a look at the basics of what Playmaker can do before trying to take on something a little more advanced. Playmaker is great for branching dialog and not overly complex but without the basic knowledge it would be very hard.
I built a dialog system for one of my games (unreleased) which would take dialog from txt files and put them into an array for different character moods and randomly select from those responses, remove them from the array so characters wouldn't say the same thing over and over etc. I also had mood points per character and each piece of dialog would change the mood of characters ... this was just the tip of what I have planned.
Check out the basics first!