Use a different skin. Maybe the older Winamp Modern skin that came with Winamp or one of the many third party skins
from the Winamp.com database.
Bento was designed to be a SUI or "All In One" to answer the many request for a SUI skin. Separating the panels would pretty much defeat the purpose of a SUI skin. If you like to look of Bento, but want separate windows, you could try the Bento Classified
skin. As it is a Classic Skin version of Bento it will not have Bento's modern skin features, such as the File Info panel and Notifications bubble.