The easiest method of transferring your music and pictures is to move the libraries to an external hard drive and then simply drag and drop them into your iMac. Very very simple to do.
Migration Assistant is a tool that will migrate much more information however it doesn't give your the choice of picking and choosing what files you want, that is why I'd suggest my approach. I'd strongly recommend you bookmark and read Apple's Mac Basics, it's located at:
https://www.apple.com/support/macbasics/
In that link you will find information that advises of the different methods of migrating from a PC to a Mac. I've found that following Apple's instructions is the best approach. I made the switch from PC's to Macs about 6 years ago now and have never looked back. If you are pretty familiar with MS Windows you
shouldn't have too much trouble, there is a learning curve but it's not steep. And if you are like most users after a couple of months you will find yourself saying, "why didn't I do this years ago!"
BTW if you are interested in learning about Migration Assistant please read Pondini's article, it's the definitive standard for explaining Setup Assistant and Migration Assistant. The link is:
http://pondini.org/OSX/MigrateLion.html