It seems that not all internal formats are implemented. I'm expecting these two calls to produce the same texture rendering:
Code :
glTexImage(..,GL_RGBA4, ..., GL_RGBA, GL_UNSIGNED_BYTE, dataPtr); // texture 1
glTexImage(..,GL_RGBA4, ..., GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4, dataPtr); // texture 2
Result (texture1 above and texture2 below)
Click image for larger version. 

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I've also noticed problems for RGBA2 and R3_G3_B2 internalformats.
Latest source code, makefiles and vs2010 solution available here:
I've only tested on linux, would be nice if someone could give feedback for windows as well.