Sexual selection is natural selection, true. But sexual selection can be given an unambiguous definition, namely when the selective force is the choice exerted by potential mates. If peahens chose peacocks with flashy tails over those with drab tails, then big, flashy tails is a result of sexual selection. But you are correct - it is still natural selection in that the reason males' tails are big and flashy is because males with flashy tails are more likely to produce offspring than males with drab tails.
Edited to add:
The difference is that in sexual selection the driving selective force is explicitly specified.
[This message has been edited by Chiroptera, 04-18-2004]
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