Depending on which version you have, use the background eraser. If there is enough contrast between the image you are trying to obtain and its background, it's a piece of cake. You may have to adjust the pixel tolerance. The lower the number, the better PS discerns the difference between the image and the background. Other methods are the magic eraser--which is good if you want to remove a solid background, or the magnetic lasso which tries to select your image based on its borders. If you own Photoshop, look under the help menu where there is a tutorial for every tool on the palette.
