that's the way Valve optimized HL2 on FX cards by running them in DX8 mode!!
you should modify the dxsupport.cfg file to force DX9 on your card, it was very hot topic when discovered last month.
http://forums.guru3d.com/showthread....postid=1014127
original thread:
http://forums.guru3d.com/showthread....hreadid=115614
and some comments:
http://www.nvnews.net/vbulletin/showthread.php?t=41625