open Itunes and open the music file in your SG2 and drag and drop the album into the music folder on your phone. SG2 plays mp4 and many other formats so you don't have to convert the music to mp3, you might have to make a new folder for each album you put in phone so they will be easily identified if you later want to delete them FOR EXAMPLE :-
say I wanted to put Aha's - Hunting high and low album on my phone I would make a folder called that in my SG2 music folder and then I would just drag the album cover in my Itunes over to said new folder.repeat with new folder names and just keep dragging and dropping.
or if your music folder on your computer is in album format what i mean by that is that you have manually added albums to itunes so the albums will be in the right order and not messed around by Itunes you can drag and drop them in that way
hope that helps