I can't download or even preview my pictures in my digital sony dsct100 camera even when using a card reader... I am running xp windows.. please help..

You might need the software that came with the camera in order to do this. With all the digital cameras I've ever had you have to have some sort of software for the digital camera to be able to download the photos to. What came with your camera? Any type of disc? Also you need to consult your owner's manual to see what steps you've skipped.