UPDATE
I deleted my previous answer because of the news below…
Big news for those who haven’t heard. Apple has released the 2010 WWDC session videos to all members of the iphone developer program. One of the topics discussed is how they created the photos app!!! They build a very similar app step by step and have made all the code available for free.
It does not use private api either. Here is a link to the sample code download. You will probably need to login to gain access.
Check This
And, here is a link to the iTunes WWDC page:
Check This