[Galaxy S I9000 Q&A, Help & Troubleshooting] Zorigo:
Install XXJVU firmware - Here

Then Install Semaphore 2.5.0 - Thread Here - Direct Link to Semaphore 2.5.0 Here

Note that XXJVU isn't the latest 2.3.6 firmware, XXJW6 is. If you wanted to install that then the procedure is essentially the same you'll just need the XXJW6 files and CF-root or semaphore kernel for XXJW6 (i'm not sure if there is a semaphore kernel for XXJW6). But running a rooted XXJVU firmware is good enough, especially if you're gonna flash a custom rom. There aren't many differences between XXJVU and XXJW6

Here's some detailed instructions on the process;

Before you flash:

1.Backup all your important files and data

2. Download the JVU stock firmware and the (Download links provided above)

3. Make sure your phone is fully charged.

4.Disable and kill the Kies process from task manager in windows on your pc. It will interupt the flashing process.

5.This guide is strictly for Samsung Galaxy S i9000 only.

*Caution

Update your phone at your own risk. I am not, nor is anyone else, responsible for any damage of your devices arising from your usage on this tutorial or guide.

How to install JVU stock Firmware:

First, you need to flash the JVU stock firmware using odin.

After downloaded, extract the folder. The files included as followed:

CODE_I9000XXJVU_CL851880_REV03_user_low_ship.tar.md5

GT-I9000-CSC-MULTI-OXAJVU.tar.md5

MODEM_I9000XXJVU_REV_00_CL1092175.tar.md5

s1_odin_20100512.pit

Odin3

Launch the Odin3.

Put all the files into the respective fields in Odin3.

PIT: s1_odin_20100512.pit

PDA: CODE_I9000XXJVU_CL851880_REV03_user_low_ship.tar.md5

PHONE: MODEM_I9000XXJVU_REV_00_CL1092175.tar.md5

CSC: GT-I9000-CSC-MULTI-OXAJVU.tar.md5

Tick the Re-Partition

Reboot your phone into download mode (Press volume down + Home +Power Button). Yellow triangle will shown when reboot into download mode.

Connect your phone with PC via USB cable. Yellow ID:COM will shown if your device is detected.

After all the files are set, then click Start and your phone will be installed with JVU stock firmware.

After success, your phone will be reboot and JVU is installed. The setup wizard will shown up when as the phone rebooted, and make sure no boxes are ticked. If any boxes are ticked as default, please un-tick it. You can change your settings later.

Warning. Do not tick any box at first boot on set-up wizard!!! You can change the setting manually later. If the box is tick as default, please un-tick it.

How to install custom kernel (semaphore)?

Download the semaphore kernel.

Assume the Odin3 is still open, click Reset to reset all the field.

Put the downloaded ZIP files at PDA section

PDA: Semaphore_kernel_JVU_2.5.0beta.tar

Make sure the Re-partition is now un-ticked.

Reboot your phone into download mode (Press volume down + Home +Power Button). Yellow triangle will shown when reboot into download mode.

Connect your phone with PC via USB cable. Yellow ID:COM will shown if your device is detected.

After all the files are set, then click Start. It takes about 10 seconds and your phone will reboot.

Semaphore icon will be added in your phone's app menu. Go to setting and check the kernel version.