Assuming Pakistan actually has nuclear warheads mounted on missiles, you can bet that the locations of these weapons are attracting Al-Quaeda like flies to a dungpile.

A nuclear missile, already in the hands of Muslims which could--perhaps--be turned to the Dark Side, would be an ideal tool.

Terrorists launching the missile without the knowledge of the Pakistan government from Pakistani territory at a previously-targeted point in India may not be that difficult a proposition. Do they have all the safeguards that U.S. and Soviet missiles have?

Other tactics, in increasing order of difficulty would be retargeting from that launch site to a new target in range, and then, most difficult, swiping the missile and taking it out of the country. This last would be nearly impossible without the Pakistani government's cooperation, and I don't think they'll get it.

At this point, the only real terrorist tactic using these missiles would be to start a nuclear war with India. Nobody else of interest is really in range. Still, this may be nasty enough by itself.

The Pakistani missiles tested recently, the most likely existing nuclear arsenal if any, had a range of about 180 km. Supposedly, tests have been done on an 800 km. range missile, and work is being done on one with a range of 2,000 km. This last would still not reach Israel, although it would reach a lot of the Arab world. The 800 km missile would cover most of Afghanistan.