One way to do it is to pull your SD card out of the phone (assuming you have them stored on the SD card). Mount the card in a USB reader and pull them off that way. The photos will be in the DCIM folder.
If you want to pull them from the phone and leave the card in place, connect your phone to your PC with a Micro USB cable. The Galaxy S should be detected by your machine and load a USB driver that allows it to be seen by the PC.
The Galaxy S will ask you if you want to use it as a mass storage device, select "yes"