This is a short post with the few steps I used to install Jillie Bean beta3 ROM.
To be clear, this is NOT Android 4.1, Jelly Bean!

Using Odin to flash firmware

I used Odin3_v1.84 (source) to flash S5830i_XXLH2_OXXLH1_XXLH2_by_Domnic79.zip (Europe(Spain) Multi Package Firmware. Released in August.; source).

USB driver

The SAMSUNG_USB_Driver_for_Mobile_Phones.exe to get your phone connected in download mode to your computer.

The Jillie Bean beta3 ROM

And finally the zip file Jillie Bean beta3 Ace i.zip.

The instructions from the Jillie Bean forum thread:

-Install fresh ROM with ODIN
-Reboot your phone in to Recovery Mode
-Install CWM 5.0.2.6 temp
-Wipe data, cache and dalvik-cache
-Install Jillie Bean beta3 ROM
-Reboot your phone
-If not want to work then:
*Do the same
*After that wipe /data, /cache and dalvik-cache again
*Reboot your phone
*IT MUST BE WORK !!

Some screenshots of the ROM on my phone

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