Wendy - If your aim is to complete I wouldn't worry about doing pace work. That can come in training for future events if you wish. Pace work helps you get faster, but if you are new to marathon training you'll no doubt find that steady running alone will help with that.
I'd only recommend throwing in some speed work if you've been running regularly for a while before embarking on your marathon adventure.
Like Orbutt I don't follow an official plan and use one I cobbled together myself over the years. I tend to run all my shorter mid-week runs hard/fast and then take it easy for my long runs. I can do that now after years of experience, it would have killed me if I tried that for my first.