A good way to go, also, is to make sure you get your SDI (integrated defense) built. If you can manage that, the AI will not be able to hurt you as badly. If your enemy has his built, find out which city it is in, attack and destroy that city with a ground assault, then let the nukes fall!
One other thing that you can do to pass the time in some scenarios... load up on tac nukes. Its not terribly hard to make some cities into three-turn tac nuke pumps in late game. Hide them away in some corner of your empire for the big day. Once you launch all your ICBMs and the AI counter-attacks, or if the AI was first to start the GTW, the tac nukes will be safe outside the cities. Rail them to the front and commence secondary/retaliatory bombardment.
A few rules I follow when I have trigger-happy nuclear neighbors:
1) Keep your armies and all the attack units you can muster fortified away from your cities as much as possible. I almost always have some unused desert or mountain tile somewhere in my empire.. occupy them with a couple of massive modern armor and artillery stacks.
2) Figure out which of their cities have nukes in them, as well as the SDI, BEFORE the conflict, so if they start anything you know what to go after first.
3) Avoid starting nuclear war without your SDI built, unless you have control of the world uranium or aluminium supply. Avoiding nukes altogether is the best option, though.
4) Learn to accept massive global warming and rediculous IBTs