Pixel Shaders.......

Huh? You can use pixel shaders with OpenGL.

Where did you hear that? Pixel shaders are supported in both, though OpenGL refers to them as "Fragment" shaders (A more technically correct term, IMHO).

In general there are very few things DirectX can do that OpenGL can't, and vica-versa.

DX and GL are different API wrapping the same hardware.
With GL you have to look at the concept of extension (functions dynamically linked at runtime)
And dont worry about GL because it's used worldwide not only to make games. [smile]

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Original post by Anonymous Poster from what I understand is a shader in ogl or d3d is a scripting language that is supposed to compile down to the native gfx card shader assembly, am I correct here?

Pretty much, although GLSL/HLSL/Cg are not really scripting languages.

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if I am, is it better to learn specific assemblies for performance purpose??

No. HL shaders are potentially faster, as the compiler can optimize the output ASM specifically to the 3D chipset it happens to run on.