d3d10 alpha testing

That's correct, you can use clip() or discard for alpha testing in d3d10 to work how alpha testing did in d3d9.

EDIT:
Its potentionally more efficient this way, as alpha testing early in your shader can allow you to skip the rest of a possibly large shader.

There is no more fixed-function pipeline in DX10, so everything that used to be done automatically for you before (such as alpha testing) now needs to be done by your shaders. Check out the FixedFuncEMU sample in the SDK to get an idea of what else needs to be emulated.