Zumo User Forums

Do my need to take the sd card out of my unit to add songs

No, you can transfer the music with the Zumo connected to your computer, but probably should not be running Express or Basecamp as they may put locks on access(though I don't know for certain).
You do need a folder named "mp3" in the root of the sd card, other than that it's just copy/paste from your computer to the mp3 folder.
You can have sub folders for sorting your music if you would like. I have mine sorted 1st by Genre, then by individual artist.
The XT will still see all the files and allow you to select how you want them played.

Note: If you have any .mp3 files in the internal memory /mp3 folder, the Zumo won't show you the SD card as a source for playing music.