For connecting your Samsung Galaxy S to your PC you need to download and install the Samsung Galaxy S USB driver package. It is highly recommended to always use the latest version of the USB driver and you should always check whether you have the latest driver installed.
Depending upon whether your machine is running 32-Bit operating system or a 64-Bit operating system, you need to install the correct USB driver. Installing a 32-Bit version of Samsung Galaxy S USB on a 64-Bit machine or vice versa can cause operating problems.
In case you are not sure whether the version of Samsung Galaxy S USB which you are about to install is the right one, you should first create a system restore point so that you can undo any changes which are made during the installation.