Here is what i did for clean installation:
A. What i need:
1. Download latest stock firmware for GT-i9100G base on local (country) version
here
2. Download SuperAtmos Kernel V3.1
http://xdaforums.com/showthread.php?t=1369977
3. Download Superrrom V3.0
here
4. Download Superrom V3.1
http://xdaforums.com/showthread.php?t=1374135
5. Download odin
http://xdaforums.com/showthread.php?t=1365805
B. Flashing Stock Firmware:
1. Extract downloaded latest stock firmware of GT-i9100G
2. Flash .tar as PDA through odin
3. Restore factory setting and format usb (will clean all your data plz backup if necessary)
All clean now back to New
C. Flashing Superatmos kernel v3.1 (Based on XXLA1)
1. Flash Superatmos kernel v3.1 .tar as pda through odin
2. Reboot ...kernel done....
D. Flashing Superrom V3.0 (Use Restore Method):
1. Extract Superrom V3.0.zip then You will find a folder
2. Create new folder tree on internal sdcard /clockworkmod/backup/ (not micro sd!!)
3. Copy Superrom V3.0 folder to /sdcard/clockworkmod/backup/
4. Reboot into CWM recovery
5. Wipe Data/Factory Reset
6. Wipe Cache
7. wipe dalvik-cache and fix permissions
8. Go to backup/restore option
9. Select SuperROM_v3.0 and RESTORE
10. Reboot ....Superrom V3.0 Done...
E. Flashing Update Superrom v3.1:
1. Copy Superrom V3.1.zip to sdcard (no need to extract the zip)
2. Reboot into CWM recovery
3. Go to Install zip from sdcard and then choose zip from sdcard
4. Select SuperROM_v3.1 then flash it!
4. Reboot ....Updating Done.....
That's all.. hope this will help..