My manager was very happy I popped in to say "hi". Also when she interviewed me, she said it was clear from my resume that I was "passionate" about this field. I gave reasons why, and I would suggest you do the same- why do you want to work in this field? It's not enough to just love babies, and to feel that this is a happy department- it isn't always. I tend to correct people when they say "ah, you switched from cardiac to babies, I bet it's such a happy place, the happiest place in the hospital!" Well, yes it's happier than say the oncology unit. Generally it's good, but as one L&D nurse said "on a sad day here it's the saddest place in the hospital". So yes, it's not all rosy baby bottoms. Give reasons why you are passionate about this field- you are interested in the direction that the whole field is going with Baby Friendly Initiave (look it up, my manager was pleased that I didn't have a lick of experience but knew what that was) rooming in, and breastfeeding trends.
Another thing I did was join AWHONN- it's not cheap, per se, but you get magazines that discuss a lot of what you'll be concerning yourself with in OB. That's another thing my manager liked, was that before I ever had experience in OB, I joined an organization. I familiarized myself with IBCLE, La Leche League and other pertinent organizations.
I guess what I mean is do your research. Think about why you want to go into this field because I guarentee they will ask you this and they will look for an answer that reflects some background. Also, I would highly suggest looking into the program, learning about it, learning about the hospital or facility that is offering it. They may ask you what you know about it, and it looks very good to know a good deal about it. Bringing up points about the facility that you appreciate always looks good to a manager. (My hosptial is very urban, with a huge muticultrual client base and that was a big talking point during my interview, as well as my soft spot for pregnant teens and the trends in teen pregnancy).
So I hope this helps. But a word to the wise- don't hold on with all your might to this oppertunity. I have done this and have been shattered when things didn't go right. Certainly pursue it, be aggressive and hope, but don't put ALL your hope into it. (This is personal experience talking).