Flymo is right - about 85% of the population have some form of over-pronation, so this could well be seen as normal - not to be confused with Neutral.
For both Neutral and Over-Pronation you will need a different type of shoe (or if you suppinate). Even a basic gait analysis from somewhere like Sweatshop, will explain it to a basic degree and show you how each shoe will help you. I genuinely think that it is worth doing.
There are some guides online as to telling which type of gait you have, try:
http://www.runnersworld.ltd.uk/pronation.htm
http://www.nbwebexpress.com/achieve_...nning_gait.asp