SGS2 I9100 Guide: Installing Driver

My Samsung Galaxy S2 wasn't bundled with Driver CD.
But it's not really that hard to find the driver. 

You can get the driver from Samsung by downloading the full KIES software, which includes the SGS2 driver.
You can download latest KIES from here.
But actually you don't really need to download the full KIES to install the driver.
If you're using Windows 7, you can download the driver from windows update, and it works well for me.

If you only need the driver, and somehow Windows 7 didn't ask for update, you can download it manually from here.
Just point the driver folder when it asks for device driver. 

I myself enable the USB debugging on Applications>Development. This way, your device will be detected as mass storage when you connect to PC via USB.
If you didn't enable USB debugging, you need to use Wireless and network>USB utilities, and connect storage to PC to enable mass storage before connecting to PC.