when you open easy studio don't you get to see on the top row of options either Manage Files or Explore Files (don't remember the exact phrase as it's not installed on this pc but on my other)
then you simply navigate to the fie you want on the bottom file structure (your PC) and copy the music file to the top file structure (your phone)
that's how my Samsung D600 works anyway
-------------------- XP Home
Office Pro + FrontPage, IE6
AVG, Zone Alarm