as puesto el .zip tal cual en la memoria interna del movil? sin descomprimirlo ni nada.
Put Root-i9001-Signed.zip into internal sdcard
Reboot into Recovery mode
Use Volume buttons to choose apply update from sdcard in Recovery Menu.
Press Home button to submit.
Use Volume buttons to choose Root-i9001-Signed.zip on sdcard
Press Home button to start update.
2 seconds and Root is installed.
Choose reboot system now and press Home button to reboot your phone.
Algun paso no lo haces correctamente.