The driver is provided from Samsung, but you may ask where it is?
Solution 1: Install the Samsung Kies
Yes, you should download it from the Samsung website. They does not ship stupid driver CD (which will always be outdated and make packing larger) with the phone. I've never tried, but it should install the driver for you automatically (with some stupid software you may not want to pollute you PC).
Solution 2: Extract it from the Samsung Kies and install manually.
It is the way I did.
- Download the Kies from the Samsung website.
- Download and install 7-Zip
- Open the Kies_184.108.40.20693_82.exe (or newer) with 7-Zip
- Browse for CabFile\USB Driver\SAMSUNG_USB_Driver_for_Mobile_Phones.exe.cab, right click and press "Open Inside"
- Right-Click on the SAMSUNG_USB_Driver_for_Mobile_Phones.exe again and click "Open Inside"
- Extract the folder to a temporary folder
- Enable the USB debugging mode on your lovely Galaxy S (better after lagfix), you can find it from "Setting > Application > Development"
- Connect with USB
- Windows may try to locate the driver; and fail
- Open Device Manager and find the device
- Update driver, and give her the path of the temporary folder
- Repeat step 11 twice for Modem and ADB
- Done !!
Solution 3: Google it and get
You may ask, why not just Google it rathern then extract from the installation file? You can. But not everyone want to install system driver from a untrusted source. Also, the up-to-date driver makes you happier.
UPDATE: 9th July 2011
Solution 4: Get it from Samsung Developer website
Today I just found they are giving the USB driver only download from their website at http://innovator.samsungmobile.com/down/cnts/toolSDK.detail.view.do?platformId=1&cntsId=9480
You will be required to signup an account (for free) before download.