I would like you all to spread this word because it works for me after many failed tries. so the story goes:
1. update to latest Kies (Kies also at the end of installation installs latest SAMSUNG_USB_Driver_for_Mobile_Phones
2. download SAMSUNG_USB_Driver_for_Mobile_Phones_v1_3_2300_0 version driver (pls find link, google it or something thats how i do it but i didn't save the link
3. instal that version driver (if it asks you few things you confirm all and just make sure you install it
4. turn usb debbuging ON on your Galaxy s2 i9100, make sure that the phone is not in lock screen i.e. unlock it to home screen, and connect it via usb cable.
5. when the windows installs all components (Samsung adb interface is last one) and says is ready to use, pop up will come "Open devices to view files", and you open "Phone"
6. start Kies and wait to connect, phone must be again while connecting in Home screen mode (connects in less than 10 seconds for me, also if the opened Phone dir is in the background I bring it up while the kies is connecting).
THATS IT! Try it, test it, and paste it wherever you can and make the life easier to people. Cheers!
p.s. i will sum up the most important things:
1. MUST HAVE installed SAMSUNG_USB_Driver_for_Mobile_Phones_v1_3_2300_0
2. MUST HAVE usb debbuging option ENABLED
3. MUST BE in home screen mode, NOT LOCKSCREEN