Motorola Droid doesn't support content protected with DRM (Digital Rights Management). Motorola Droid allows to play DRM-free .mp3, .aac, .wma, .ogg, .wav music and .3gp .mp4 video files.

If you have DRM-protected content from Amazon Video on Demand, as well as iTunes, eMusic, Napster, Rhapsody, Nokia Music Store, Spiralfrog, Bearshare, Puretracks, MusicGiants, Cinema Now, Movielink, Microsoft Zune MarketPlace,... you need to remove DRM protection before you can use audio and video files on your Motorola Droid.

See also:
Removing DRM from Amazon VOD
How to transfer music and videos onto Modorola Droid using Motorola Media Link