why do dogs chase cats?

Cats run simple, its kicks in the hunt instinct in most dogs, ever see a cat who DIDNT run and faced up to the dog, most dogs will back down, they dont want to normally fight their prey ;o)

I have a english springer spaniel and 2 cats and they get on fine together, there has never been any problems between them. In fact they are very close as they all curl up in the dogs bed together. I honestly think that it will depend on each dog, as if they are brought up together they should get on fine. My parents also have 2 dogs and 4 cats (3 of the cats were strays that just decided to move in) and even though they wernt brought up tohgether they are still fine together. I think it will depend totally on the temprament of the cat and dog,however i do believe that if they are introduced to the other at a young age they should get on fine together.