I use X4500 (G41) on Windows XP with latest driver (2010/7/20 220.127.116.1184).
When glFramebufferTexture2DEXT() is called after a new frame buffer object is created and bound (thus not frame buffer complete yet), it generates an OpenGL error 0x0506 (GL_INVALID_FRAMEBUFFER_OPERATION).
It seems to me that such error is inappropriate, and I think it is not an error at all.
That frame buffer object works fine.
Same program works as intended with nVidia GPU which does not generate any error at this point.