turn the phone off wait for it to vibrate or the LED's to go go off. Then Hold Vol Up + Home Button +Power all at the same time when you see the boot screen (black and white text saying Samsung Galaxy S I9000) let go of power and keep holding Volume and Home and it should boot into recover mode.
Be care full if you hold the home button to long it selects reboot device and you have to do the above again.
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