OLDER TECHNIQUE: Rooting by using rooted kernel
longer steps, but seems to be working properly all the time biggrin.gif

Edit: It is possible to substitute the firmware with the latest one (DZKJ2), but you'll need the original kernel-image only tar file, which sadly I haven't be able to find at the moment sad.gif

What you'll need;

1. A Galaxy SII I9100G phone. The G is required!. Check behind your battery
2. USB cable suitable for the phone
3. Samsung driver or KIES installed. But please close KIES before proceeding Go Google if you don't have one
4. DZKI1 original full firmware: http://www.multiupload.com/6L8BALT56F
5. DZKI1 original kernel image: http://www.multiupload.com/AS18CIXQNX
6. ZCKH4 rooted kernel image: http://forum.xda-developers.com/showpost.p...52&postcount=22
7. I9100G PIT file: http://forum.lowyat.net/index.php?act=Atta...post&id=2465180
8. ODIN 1.85 firmware flasher: http://www.multiupload.com/1VELKG3NIQ

Password if required is "intratech@XDA" without the quotes

The idea;

Update your phone to the latest DZKI1 firmware, then flash a rooted ZCKH4 to get the Superuser application. (ZCKH4 is compatible with I9100Gs, although, your wifi will not work). Update the superuser application, and flash back the original DZKI1 to fix your wifi.

The Steps

Preparation
Firstly, extract everything into its own folder. Switch off the phone and take out SIM and SD card. To enter download mode, hold down Volume Down button + OK button(home) simultaneously and THEN press the Power Button. Once you see the warning logo, IMMEDIATELY release all buttons and push ONLY the Volume UP button. You'll see "ODIN MODE" and the android logo. Plug in the phone to your pc and let the new driver installation finish. WARNING, please DO NOT continue if you are having problem with the driver installation.

Updating Your Firmware
Please follow the instruction exactly, otherwise, you'll probably get into complicated problems. Get to the Odin folder and run the application. Click PIT button and browse for the "omap4_all_20110627_emmc.pit" file. Click the PDA button and include the DZKI1 original full firmware. It's filename should be .tar. Click "Start" and wait until its done. The phone will restart and you'll have a new firmware. If you stucked on the galaxy logo (NOT THE YELLOW TRIANGLE case), please google for "Galaxy s2 clear cache". If everything went smoothly, you'll be up and away setting up the google account information.

Flash The Rooted Kernel
Please follow the above instruction again, substituting the DZKI1 original full firmware with ZCKH4 rooted kernel image. Once your phone booted up, you'll be able to find the Superuser Icon;

user posted image

That's mean your phone has successfully been rooted! Yay!

But, still not done yet, because your custom kernel is causing your wifi to malfunction and the yellow triangle to appear. We'll address that by reflashing the DZKI1 original kernel image

Flash The Original Kernel Image
Just follow the "Updating Your Firmware" substituting the DZKI1 original full firmware with DZKI1 original kernel image

You'r done! Now you have a rooted phone meanwhile maintaining original firmware. YAY!!!

Thanks to intratech@XDA. You guys should buy him a beer [donate to intratech]
Intratech thread: http://forum.xda-developers.com/showpost.p...72&postcount=29