Safari 4 places its tabs at the top of the window. If you prefer Safari 3's tab location (within the window), open Terminal and copy and paste the following command to get Safari 3 style tabs back:
defaults write com.apple.Safari DebugSafari4TabBarIsOnTop -bool FALSE
To get top tabs back, quit Safari, and repeat the above Terminal command, but change FALSE to TRUE.
Mac OS X Hints
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