As muno says, DX9 is not suppossed to lower you performance.
As for the 3dmark score, don't be dissapointed, you probably have a GREAT system BUT you don't have a DX9 compliant card. The only DirectX9 cards out there are the Radeon 9500, 9500Pro, 9700, 9700Pro and the GeForce FX. 3Dmark is a synthetic benchmark.. meaning... it is not worth it.. Benchmark using games and you will see the difference.!