I think the only way it can be done is by building the maximum number of cites permissible (about 250). After this it's impossible to build new cities.
You could also increase the cost of settler/engineer units to make it more expencive for the computer to start new cities (though this may just make the computer waste its resources on the expencive settlers, and make less military units
)
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If all else fails, immortality can always be assured by spectacular error
-John Kenneth Galbraith
[This message has been edited by Case (edited December 07, 2000).]