Caution:- Please Backup your all data and settings before rooting your device.
Here is the steps to Root Samsung Galaxy S I9000 to XXJVU 2.3.6 :
Step 1: First of all, Download Android 2.3.6 Gingerbread Value Pack (XXJVU) and ODIN to your computer. After that, extract the ROM ( Use password:- samfirmware.com)
Step 2: When the files are extracted, launch ODIN on your PC and then turn off your Galaxy S.
Step3: For Boot in download mode, go to download mode by Press and hold Volume Down + Home + Power buttons.
Step 4: Now Connect your phone to your PC using a USB cable. (Before proceed to Next Step, please make sure that ODIN detect your device)
Click on Odin PIT Tab
Select the PIT – s1_odin_20100512.pit
Click on Odin PDA Tab
Select the CODE_I9000XXJVU_CL851880_REV03_user_low_ship.tar.md5 file.
Click on Odin PHONE Tab
Click on Odin CSC Tab
Step 6: Click on START in ODIN to start flash the leaked firmware on your device. And that's it.
So, now you have successfully rooted your Galaxy S running on XXJVU 2.3.6 (Android 4.0 Value Pack).