[marcus_cruz]

Connect your Diamond to your PC.
Explore your device through windows explorer.
Find the music directory on the device.
You wont be able to delete all of the files in there until you create another playlist and the files are not in use.
It's rather tricky to add media files to a playlist for playing in the sprint player. This is something you can play around with. As a previous poster stated, it's easier to just add or copy the files to the directory. I'm not sure if the player looks at the internal 4 gig storage location or not. It may.
I like to use GSPlayer. It streams through shoutcast, it also play mp3's at very good quality with surround sound simulation plus a variety of other profiles and filters.