I'm with Euro on this one. The Western grip is the same as the eastern backhand. On the Western grip. your index knuckle is way under the grip, and if yiou turn it over, its on top instead producing an Eastern Backhand, but you have to give allowances for mild eastern backhand vs. extreme. Anwyay I dont want to confuse the OP. The eastern forehand and the eastern backhand are totally different grips
OK here is how I would have you picture it. On the tennis court face the net, hold the racquet with a flat face on the forehand side facing the net as if it was about to contact an incoming ball, use your non dominant hand, ie if you are a righty use you left to hold it up. Now with your dominant hand (right for most people) put your palm face up and hold it underneath the racquet, now grip the racquet making sure your index knuckle is on the bottom. You have just produced a western grip.
Now windshield wiper the forehand to the other side making sure the same side faces the net, and then turn your body over as if hitting a backhand. you are now in an eastern backhand grip