Westies can suffer terribly with skin conditions, so if you get one, please get one from a reputable breeder, as a lot of the problems are hereditary, and as they are a popular breed, the puppy farmers always tend to have them. Make sure the breeder's older dogs have no problems. Go to the champdogs website for details of breeders in your area and have a read of several websites before you think about getting one. Also be careful if you buy one from someone who has just bred from their pet bitch as they may not have the knowledge of the dogs in the background. Go for a breeder who has several generations that they are proud to show you.
http://www.champdogs.co.uk
Click on Guided Search, then Terrier Group, then West Highland White Terriers, then Breeders.