it would really help you if you have a larger copy of that image.

if not, you can create an enlargement so you can have a bigger canvas you can work with. if you are not that familiar in enlarging images without much loss in quality, i affix herein something i came up with.

(click on thumbnail to enlarge)
then proceed in erasing the background as you wish. you can try darran's method above.
if you're interested in other techniques, you can google search for "photoshop masking tutorials".
here is one involving masking out complex objects. you can find much simpler methods, or something which would apply to photoshop CS specifically, although i would suppose you can grasp and adapt the general idea of the technique for use in photoshop CS if ever the tutorial you found is for a much earlier version.
after you have finished erasing the background you want to eliminate, you can them simply resize the image to the size you want and add your own background in a separate layer. happy photo editing!