After trying every possible way to sync music, mentioned in my signature are my adventures but i would bother reading that now, cause the best music syncing thing is by far Song Bird found here:
If you need help setting it up (its fairly straight forward though) check out my article here on Song Bird and the Droid:
Easiest Way to Sync Music to Your Motorola Droid
If you have any questions feel free to ask here. If you have ever used iTunes it pretty much works like that, just don't forget to mount your Droid. Also be sure to check out all the add ons you can get for Song Bird.