Good answers here, and hope the Valium will help you overcome your fear! And a good, understanding dentist cannot be underestimated. I hope you find one that's right for you. If the practice you are registered with has more than one dentist, you can choose to see another if you are unhappy, and let them know that you are a nervous patient so they can place you with someone gentle.
And I must stress the importance of having a chaperone with you before, during and after you take the Valium. You never know what effect it is going to have on you, and common side-effects of loss of inhibition and memory loss do not sit well together! If necessary your chaperone might have to recount some things you said or did, like a good mate after a drunken night out ;)
So stay safe, and fingers crossed, a lovely trip to the dentist.