Hi,
If you check support website you'll find Samsung USB Drivers for Mobile Phones 1.3.850 in driver section. This include your I9100 driver. Also for unlocking it you need the following.
-phone to be connected powered on in ABD mode: Settings >> Applications >> Development and select USB Debugging
-fw version lower than 2.3.3 for one click read codes
-root and patch for fw >=2.3.3 for read codes
TIPS: to root & patch your >=2.3.3 fw see post #16 it's all included 10x to danrachita
WBR,
gsm9l