I can tell you by what chip you're using if that helps. Like Matt told ya eaqrlier, the FX5600 has support for DirectX 9, which has ShaderModel 2.0 in it. The 6xxx series supports DirectX 9c, including ShaderModel 3.0. Support for ShaderModel 3.0 is part of nVidia's 7xxx series as well. Their new 8xxx series support DirectX 10, and that includes ShaderModel 4.0.
With ATi we have DirectX 9 support in the 9550 through the X850 series. The ATi X1xx series support DirectX 9c, including ShaderModel 3.0. ATi's upcoming X2xxx chips are to include support for DirectX 10, which has ShaderModel 4.0.