I believe there is a technical difference between martial law and emergency rule. I believe that in the former, the entire government is overthrown and replaced with a caretaker (and temporary) government, usually hand-picked by the new military ruler. In the latter, the government is simply authorized to do more things than before. In both cases, the constitution is suspended. (I am not sure which cases, if any, necessarily involve the imposition of a Provisional Constitutional Order, which is a sort of temporary constitution.)
(As a point of reference, Indira Gandhi, prime minister of India, had emergency rule, which was not martial law, declared, which spanned from June 25, 1975, to March 21, 1977. (This period is often known as the Emergency Raj.) This was in response to the Allahabad High Court dismissing her. That incident, and the difference between what Musharraf recently did and what he did when he initially took over in 1999, warrants a differentiation between martial law and emergency rule.)
Technically, Musharraf has imposed emergency rule and/or declared a state of emergency. He said in his address that the government will remain intact: nothing will change with regard to current governing authorities and bodies. In any case, the constitution has been suspended, and the Supreme Court has been flushed. All anti-Musharraf justices have been dismissed and detained. A new chief justice was sworn in by Musharraf. It is expected that the new Supreme Court will be assembled and sworn in soon. This time, it is expected that the Supreme Court will not challenge Musharraf or his directives.
Whether one may call this a “coup” is debatable. On the one hand, this was a coup against the Supreme Court. On the other hand, governing bodies, people, and authorities remain unchanged.