AlanHourihane started writing a 3D driver for certain trident chips. The DRI component is available in Mesa CVS; the DRM and DDX are available on the trident-0-0-2 branch on DRI CVS. It is not yet finished.
The XGI Volari V3 is also based on a Trident core.
Complete specs (2D, 3D, Overlay and MC/IDCT, capture, and dualhead) for the Trident CyberBLADE i1 (VIA Apollo PLE133 Chipset VT8601A North Bridge) http://www.viavpsd.com/product/Download.jsp?motherboardId=21
Trident Microsystems, Inc: Videographics: http://www.tridentmicro.com/videographics/index.asp