Get a Swiss Ball if you can afford it as well. At first use it to prop up your legs for the crunches. Or balance it on your bent knees and push up with your hands (which should be shoulder length apart). This will help you learn how to do the crunches properly. Later when you've developed enough strength start doing crunches on the ball.

As well as surfing the net for exercises go to your local library and look for books on pilates, balls and strength training. Or go buy some. Websites are good, but having a book to refer to I find a big help.