This shot shows Towel CVS of 7th September 2003 running on GNU/Linux. The most notable feature in this particular screenshot is the new UI design, which is based on (but not entirely conformant with) the GNOME Human Interface Guidelines, and is both clearer and more attractive. More work remains to be done on the media library as time progresses, but the major effort is complete.
GTK+ theme is Ximian's Industrial theme which they used in Ximian Desktop 2. The window manager is xfwm4 with its default theme, although it is running inside a GNOME 2.4.0rc1 desktop. Why? That's a story for somewhere else.