Thanks to InsideMicrosoft for pointing this one out: “Windows Media Player PowerToys for Windows XP”, a variety of playlist and skin importers, plus management for media libraries.
The most useful: the Windows Media Player for Windows XP Tray Control. This little gem lets you minimize the player to a tray control, that on right-click, let's you execute common tasks. For me, this is much better than the minimize to taskbar tray.
Note: these tools are unsupported by Microsoft.