Plug the Droid into your computer. Swipe down on the "Notifications" bar at the top of your home screen, and tap on the bar that says "USB connected." Click on "MOUNT." Your Droid will then show up on your Computer just like a thumb drive or external hard drive.
On your computer, go into MY COMPUTER and determine which drive is your Droid, double click it, and you'll see a Windows Explorer window showing you the contents of your Droid -- it'll have a bunch of folders, including DCIM, google-maps-navigation, albumthumbs, etc.
Create a folder called MUSIC on your Droid by right clicking inside the Droid directory on your computer, and choosing "NEW" then "FOLDER."
Find the directory on your computer that holds the Limewire MP3 files, and simply click and drag those files into the Droid's "MUSIC" folder that you just created.
Voila. Done.