Why can't i put music on my iphone?

I bought a new laptop and transferred all my files (including my music library) from my old laptop onto my new. I used Microsoft Easy Transfer. I also deauthorized my itunes account from my old laptop before I reinstalled an new OS on it. Then I authorized my itunes account on my new laptop, and synced my iPhone 4 with it. Now, I'd like to just drag and drop music into my iPhone like I used to, but it won't let me. If I go to the phone tab, I can tell it to sync with my iPhone, but then it warns that all playlists and music will be removed from the phone. I don't want to sync my entire library, as it is much too large to fit it all on my phone. Besides, I don't want to lose those playlists and as a matter of fact I'd also like to figure out if there is some way I can save those playlists onto my laptop, since with the transfer over to the new laptop it didn't bring these over, I don't think. How do I get drop n' drag to work to and from my iPhone to my laptop iTunes?